diff --git a/src/App.tsx b/src/App.tsx
index e4bc283..938f6bf 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,5 +1,6 @@
 import { useEffect, useMemo, useRef, useState } from "react";
 import { FloatingActions } from "./components/FloatingActions";
+import { ScriptNav } from "./components/ScriptNav";
 import { ScriptSummary } from "./components/ScriptSummary";
 import { ScriptView } from "./components/ScriptView";
 import { toggleCharactersByMatch } from "./lib/characterToggle";
@@ -153,6 +154,13 @@ export function App() {
         noVoice={noVoice}
         onToggleNoVoice={toggleNoVoice}
       />
+      {dialogues.length > 0 && (
+        <ScriptNav
+          dialogues={dialogues}
+          selected={selected}
+          noVoice={noVoice}
+        />
+      )}
       <FloatingActions onExportText={exportText} />
     </>
   );
diff --git a/src/components/FloatingActions.tsx b/src/components/FloatingActions.tsx
index 487e10b..42b7a3e 100644
--- a/src/components/FloatingActions.tsx
+++ b/src/components/FloatingActions.tsx
@@ -3,34 +3,10 @@ type Props = {
 };
 
 export function FloatingActions({ onExportText }: Props) {
-  const scrollToStart = () =>
-    window.scrollTo({ left: 0, top: 0, behavior: "smooth" });
-  const scrollToEnd = () =>
-    window.scrollTo({
-      left: -document.documentElement.scrollWidth,
-      top: 0,
-      behavior: "smooth",
-    });
   const handlePrint = () => window.print();
 
   return (
     <div id="floatingActions">
-      <button
-        type="button"
-        onClick={scrollToStart}
-        title="先頭に戻る"
-        aria-label="先頭に戻る"
-      >
-        →
-      </button>
-      <button
-        type="button"
-        onClick={scrollToEnd}
-        title="末尾に進む"
-        aria-label="末尾に進む"
-      >
-        ←
-      </button>
       <button
         type="button"
         onClick={onExportText}
diff --git a/src/components/ScriptNav.tsx b/src/components/ScriptNav.tsx
new file mode 100644
index 0000000..100f471
--- /dev/null
+++ b/src/components/ScriptNav.tsx
@@ -0,0 +1,176 @@
+import { useEffect, useState } from "react";
+import { findAdjacentDialogue } from "../lib/scriptNav";
+import type { Dialogue } from "../types";
+
+type Props = {
+  // 内容は使わず、ハイライト集合が変化したら可否を再計算するための依存として受け取る
+  dialogues: Dialogue[];
+  selected: Set<string>;
+  noVoice: Set<number>;
+};
+
+type NavState = {
+  areaCenter: number | null;
+  atStart: boolean;
+  atEnd: boolean;
+  canNext: boolean;
+  canPrev: boolean;
+};
+
+// 読める領域の右端 x を返す。サマリ（キャラリスト等）は右側に sticky で
+// 居座るため、その左端までを読める領域とみなす。サマリが無ければビューポート幅。
+function readAreaRightEdge(): number {
+  const summary = document.getElementById("scriptSummary");
+  if (!summary) return window.innerWidth;
+  const rect = summary.getBoundingClientRect();
+  const marginLeft = parseFloat(getComputedStyle(summary).marginLeft) || 0;
+  return rect.left - marginLeft;
+}
+
+function highlightPositions() {
+  const els = Array.from(
+    document.querySelectorAll<HTMLElement>(
+      "#scriptContainer .character-dialogue.highlighted",
+    ),
+  );
+  return els.map((el) => {
+    const r = el.getBoundingClientRect();
+    return { id: Number(el.dataset.dialogueId), center: r.left + r.width / 2 };
+  });
+}
+
+// 指定の scrollX まで素早く（250ms）スクロールする。
+// 縦書き（vertical-rl）では scrollX は負。ネイティブの smooth より速い。
+function animateScrollX(targetLeft: number) {
+  const startLeft = window.scrollX;
+  const dist = targetLeft - startLeft;
+  if (dist === 0) return;
+  const duration = 250;
+  let startTime: number | null = null;
+  const step = (now: number) => {
+    if (startTime === null) startTime = now;
+    const t = Math.min(1, (now - startTime) / duration);
+    const ease = 1 - Math.pow(1 - t, 3); // easeOutCubic
+    window.scrollTo({ left: startLeft + dist * ease, top: 0 });
+    if (t < 1) requestAnimationFrame(step);
+  };
+  requestAnimationFrame(step);
+}
+
+export function ScriptNav({ dialogues, selected, noVoice }: Props) {
+  const [state, setState] = useState<NavState>({
+    areaCenter: null,
+    atStart: true,
+    atEnd: false,
+    canNext: false,
+    canPrev: false,
+  });
+
+  useEffect(() => {
+    const recompute = () => {
+      const doc = document.documentElement;
+      const maxScroll = doc.scrollWidth - doc.clientWidth; // overflow 量（正）
+      const x = -window.scrollX; // 0（先頭・右）〜 maxScroll（末尾・左）
+      const center = readAreaRightEdge() / 2;
+      const positions = highlightPositions();
+      setState({
+        areaCenter: center,
+        atStart: x <= 1,
+        atEnd: x >= maxScroll - 1,
+        canNext: findAdjacentDialogue(positions, center, "next") !== null,
+        canPrev: findAdjacentDialogue(positions, center, "prev") !== null,
+      });
+    };
+
+    // スクロール中は rAF で間引く
+    let ticking = false;
+    const onScroll = () => {
+      if (ticking) return;
+      ticking = true;
+      requestAnimationFrame(() => {
+        ticking = false;
+        recompute();
+      });
+    };
+
+    recompute();
+    window.addEventListener("scroll", onScroll, { passive: true });
+    window.addEventListener("resize", recompute);
+    const summary = document.getElementById("scriptSummary");
+    let ro: ResizeObserver | null = null;
+    if (summary && typeof ResizeObserver !== "undefined") {
+      ro = new ResizeObserver(recompute);
+      ro.observe(summary);
+    }
+    return () => {
+      window.removeEventListener("scroll", onScroll);
+      window.removeEventListener("resize", recompute);
+      ro?.disconnect();
+    };
+  }, [dialogues, selected, noVoice]);
+
+  const scrollToStart = () => animateScrollX(0);
+  const scrollToEnd = () =>
+    animateScrollX(-document.documentElement.scrollWidth);
+
+  // ハイライト中セリフのうち、読める領域の中央から見た隣のセリフを中央へ寄せる
+  const scrollToAdjacent = (direction: "next" | "prev") => {
+    const center = readAreaRightEdge() / 2;
+    const positions = highlightPositions();
+    const targetId = findAdjacentDialogue(positions, center, direction);
+    if (targetId === null) return;
+    const target = document.querySelector<HTMLElement>(
+      `#scriptContainer [data-dialogue-id="${targetId}"]`,
+    );
+    if (!target) return;
+    const r = target.getBoundingClientRect();
+    // 対象の中心を読める領域の左右中央へ。目標 scrollX を直接指定して正確に合わせる
+    animateScrollX(window.scrollX + (r.left + r.width / 2 - center));
+  };
+
+  return (
+    <div
+      id="scriptNav"
+      style={{
+        left: state.areaCenter != null ? `${state.areaCenter}px` : undefined,
+      }}
+    >
+      <button
+        type="button"
+        onClick={scrollToEnd}
+        disabled={state.atEnd}
+        title="最後へ"
+        aria-label="最後へ"
+      >
+        «
+      </button>
+      <button
+        type="button"
+        onClick={() => scrollToAdjacent("next")}
+        disabled={!state.canNext}
+        title="次のセリフへ"
+        aria-label="次のセリフへ"
+      >
+        ‹
+      </button>
+      <button
+        type="button"
+        onClick={() => scrollToAdjacent("prev")}
+        disabled={!state.canPrev}
+        title="前のセリフへ"
+        aria-label="前のセリフへ"
+      >
+        ›
+      </button>
+      <button
+        type="button"
+        onClick={scrollToStart}
+        disabled={state.atStart}
+        title="最初へ"
+        aria-label="最初へ"
+      >
+        »
+      </button>
+    </div>
+  );
+}
diff --git a/src/components/ScriptView.tsx b/src/components/ScriptView.tsx
index a1fc609..837d5c0 100644
--- a/src/components/ScriptView.tsx
+++ b/src/components/ScriptView.tsx
@@ -36,6 +36,7 @@ export function ScriptView({
           <button
             key={d.id}
             type="button"
+            data-dialogue-id={d.id}
             className={
               "character-dialogue" + (highlighted ? " highlighted" : "")
             }
diff --git a/src/index.css b/src/index.css
index ddb467e..d3c6fa4 100644
--- a/src/index.css
+++ b/src/index.css
@@ -84,7 +84,6 @@ button.character-dialogue:disabled {
 
 /* サマリのスタイル */
 #scriptSummary {
-  margin-left: var(--page-margin);
   margin-block-start: calc(-1 * var(--page-margin));
   padding-block-start: var(--page-margin);
   position: sticky;
@@ -92,16 +91,6 @@ button.character-dialogue:disabled {
   background: white;
   z-index: 10;
 
-  &::after {
-    content: "";
-    position: absolute;
-    top: 0;
-    bottom: 0;
-    left: calc(-1 * var(--page-margin));
-    width: var(--page-margin);
-    background: linear-gradient(to right, transparent, white);
-    pointer-events: none;
-  }
   input,
   textarea {
     font: inherit;
@@ -291,6 +280,39 @@ button.character-dialogue:disabled {
   color: white;
 }
 
+/* 台本下部中央のセリフ送りナビ */
+#scriptNav {
+  position: fixed;
+  bottom: 16px;
+  left: 50%;
+  transform: translateX(-50%);
+  display: flex;
+  gap: 8px;
+  z-index: 100;
+  writing-mode: horizontal-tb;
+}
+#scriptNav button {
+  width: 40px;
+  height: 40px;
+  border-radius: 50%;
+  border: 1px solid var(--highlight-color);
+  background: white;
+  color: var(--highlight-color);
+  cursor: pointer;
+  font-family: var(--font-sans);
+  font-size: 18px;
+  line-height: 1;
+  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.15);
+}
+#scriptNav button:hover:not(:disabled) {
+  background: var(--highlight-color);
+  color: white;
+}
+#scriptNav button:disabled {
+  opacity: 0.4;
+  cursor: default;
+}
+
 /* 印刷時のスタイル */
 @media print {
   @page {
@@ -312,4 +334,7 @@ button.character-dialogue:disabled {
   #floatingActions {
     display: none;
   }
+  #scriptNav {
+    display: none;
+  }
 }
diff --git a/src/lib/scriptNav.test.ts b/src/lib/scriptNav.test.ts
new file mode 100644
index 0000000..741ccfb
--- /dev/null
+++ b/src/lib/scriptNav.test.ts
@@ -0,0 +1,39 @@
+import { describe, it, expect } from "vitest";
+import { findAdjacentDialogue } from "./scriptNav";
+
+// start 寄り（右・中心大）から end 寄り（左・中心小）の順
+const positions = [
+  { id: 1, center: 900 },
+  { id: 2, center: 600 },
+  { id: 3, center: 300 },
+];
+
+describe("findAdjacentDialogue", () => {
+  it("next は基準より左で最も近いセリフを選ぶ", () => {
+    expect(findAdjacentDialogue(positions, 650, "next")).toBe(2);
+  });
+
+  it("prev は基準より右で最も近いセリフを選ぶ", () => {
+    expect(findAdjacentDialogue(positions, 650, "prev")).toBe(1);
+  });
+
+  it("中央のセリフからさらに next で次へ進む", () => {
+    expect(findAdjacentDialogue(positions, 600, "next")).toBe(3);
+  });
+
+  it("中央のセリフから prev で前へ戻る", () => {
+    expect(findAdjacentDialogue(positions, 600, "prev")).toBe(1);
+  });
+
+  it("next 方向に対象が無ければ null", () => {
+    expect(findAdjacentDialogue(positions, 200, "next")).toBe(null);
+  });
+
+  it("prev 方向に対象が無ければ null", () => {
+    expect(findAdjacentDialogue(positions, 1000, "prev")).toBe(null);
+  });
+
+  it("空配列は null", () => {
+    expect(findAdjacentDialogue([], 500, "next")).toBe(null);
+  });
+});
diff --git a/src/lib/scriptNav.ts b/src/lib/scriptNav.ts
new file mode 100644
index 0000000..ac114c2
--- /dev/null
+++ b/src/lib/scriptNav.ts
@@ -0,0 +1,29 @@
+export type DialoguePosition = { id: number; center: number };
+
+/**
+ * 縦書き（vertical-rl）の台本で、基準位置から見た隣のセリフ id を返す。
+ * start は右（中心 x が大きい）、end は左（中心 x が小さい）にあるため
+ * - "next"（次のセリフ＝end 方向）は基準より左で最も近いもの
+ * - "prev"（前のセリフ＝start 方向）は基準より右で最も近いもの
+ * を選ぶ。該当が無ければ null。
+ */
+export function findAdjacentDialogue(
+  positions: DialoguePosition[],
+  reference: number,
+  direction: "next" | "prev",
+): number | null {
+  const eps = 1; // 中央付近に居座るセリフを自分自身として拾わないための遊び
+  let best: DialoguePosition | null = null;
+  for (const p of positions) {
+    if (direction === "next") {
+      if (p.center < reference - eps && (!best || p.center > best.center)) {
+        best = p;
+      }
+    } else {
+      if (p.center > reference + eps && (!best || p.center < best.center)) {
+        best = p;
+      }
+    }
+  }
+  return best ? best.id : null;
+}