diff --git a/A00_Common/spreadsheet/spreadsheet_grid.css b/A00_Common/spreadsheet/spreadsheet_grid.css
index be6845e2..9998e5b2 100644
--- a/A00_Common/spreadsheet/spreadsheet_grid.css
+++ b/A00_Common/spreadsheet/spreadsheet_grid.css
@@ -183,6 +183,19 @@
   color: #c00;
 }
 
+/* 오류 칸 — 엑셀 오류 검사 초록 세모(왼 위 · sub3 오류 까닭은 title 풍선). */
+.aislo-cell.is-error::before {
+  content: "";
+  position: absolute;
+  top: 0;
+  left: 0;
+  width: 0;
+  height: 0;
+  border-style: solid;
+  border-width: 6px 6px 0 0;
+  border-color: #2e7d32 transparent transparent transparent;
+}
+
 .aislo-cell.is-selected {
   outline: 2px solid var(--aislo-grid-selected);
   outline-offset: -1px;
diff --git a/A00_Common/spreadsheet/spreadsheet_grid.ts b/A00_Common/spreadsheet/spreadsheet_grid.ts
index 6f455663..3dc806f1 100644
--- a/A00_Common/spreadsheet/spreadsheet_grid.ts
+++ b/A00_Common/spreadsheet/spreadsheet_grid.ts
@@ -34,6 +34,7 @@ import {
   type LineGeometry,
   type OutlineRun,
 } from "./spreadsheet_headers";
+import { resolveCondFmtStyle, type CondFmtValue } from "./spreadsheet_condfmt";
 import { formatValue } from "./spreadsheet_numfmt";
 import { MAX_COLS, MAX_ROWS } from "./spreadsheet_types";
 import type {
@@ -150,6 +151,23 @@ interface CellDisplay {
   color?: string;
 }
 
+/** 칸 하나 값 — 식이면 엔진 값 · 아니면 입력 값(수는 Frac로) · 둘 다 없으면 빈 칸. */
+function scalarAt(ctx: SpreadsheetContext, sheet: Sheet, r: number, c: number): Scalar {
+  const cell = sheet.칸[toA1(r, c)];
+  return cell?.식 !== undefined
+    ? ctx.engine.value(sheet.id, r, c)
+    : cell?.값 !== undefined
+      ? toScalar(cell.값)
+      : null;
+}
+
+/** 조건부 서식(sub4) 이 값을 보는 형 — Frac 는 근사 수로(조건 비교용 · 오류는 조건 대상 아님). */
+function toCondFmtValue(scalar: Scalar): CondFmtValue {
+  if (scalar === null || typeof scalar === "boolean" || typeof scalar === "string") return scalar;
+  if ("error" in scalar) return null;
+  return Number(scalar.n) / Number(scalar.d);
+}
+
 function cellDisplay(
   ctx: SpreadsheetContext,
   sheet: Sheet,
@@ -158,13 +176,7 @@ function cellDisplay(
   hAlign0: HAlign,
   code?: string,
 ): CellDisplay {
-  const cell = sheet.칸[toA1(r, c)];
-  const scalar: Scalar =
-    cell?.식 !== undefined
-      ? ctx.engine.value(sheet.id, r, c)
-      : cell?.값 !== undefined
-        ? toScalar(cell.값)
-        : null;
+  const scalar = scalarAt(ctx, sheet, r, c);
   const formatted = formatValue(scalar, code);
   const isError = typeof scalar === "object" && scalar !== null && "error" in scalar;
   const hAlign: HAlign = hAlign0 !== "general" ? hAlign0 : formatted.정렬;
@@ -365,7 +377,13 @@ export function createGrid(ctx: SpreadsheetContext): GridHandle {
         cellEl.dataset.c = String(c0);
         const addr = toA1(r0, c0);
         cellEl.dataset.addr = addr;
-        const style = cellStyleAt(book, sheet, r0, c0);
+        const baseStyle = cellStyleAt(book, sheet, r0, c0);
+        const condStyle = sheet.조건부서식?.length
+          ? resolveCondFmtStyle(sheet, r0, c0, {
+              value: (rr, cc) => toCondFmtValue(scalarAt(ctx, sheet, rr, cc)),
+            })
+          : null;
+        const style = condStyle ? { ...baseStyle, ...condStyle } : baseStyle;
         const borders: ResolvedBorders = resolveBoxBorders(
           book,
           sheet,
@@ -378,7 +396,8 @@ export function createGrid(ctx: SpreadsheetContext): GridHandle {
         );
         const display = cellDisplay(ctx, sheet, r0, c0, style.가로 ?? "general", style.형식);
         applyCellStyle(cellEl, style, borders, display.hAlign, zoom);
-        if (display.color) cellEl.style.color = display.color;
+        // 조건부 서식 글자색이 이기고(엑셀과 같음) · 없으면 숫자 형식([Red] 등)이 정한 색.
+        if (display.color && !condStyle?.글자색) cellEl.style.color = display.color;
         const comment = sheet.comments?.[addr];
         setCellText(cellEl, display.text, display.title || comment || undefined);
         cellEl.classList.toggle("is-error", display.isError);
diff --git a/resources/tester/spreadsheet/spreadsheet_grid_test.ts b/resources/tester/spreadsheet/spreadsheet_grid_test.ts
index 44c80247..53d9d3be 100644
--- a/resources/tester/spreadsheet/spreadsheet_grid_test.ts
+++ b/resources/tester/spreadsheet/spreadsheet_grid_test.ts
@@ -35,9 +35,18 @@ const sheet: Sheet = {
     A6: { 값: "선택 영역 가운데(centerContinuous) 보기", 서식: 5 },
     A8: { 값: "hair 테두리 칸", 서식: 3 },
     B8: { 값: 3.14159, 서식: 7 },
+    G9: { 식: "1/0" },
     J10000: { 값: "맨 끝 칸(1만 행 스크롤 확인용)" },
   },
   comments: { H4: "메모 — ROUNDDOWN 끝수 확인" },
+  조건부서식: [
+    {
+      id: "cf1",
+      범위: [{ r0: 3, c0: 7, r1: 3, c1: 7 }],
+      조건: { 종류: "비교", 연산: "보다작음", 값: 0 },
+      스타일: { 채움: "#ffe0e0", 글자색: "#c00000", 굵게: true },
+    },
+  ],
   병합: ["A1:H1", "B8:C9"],
   열: {
     A: { 폭: 14 },
@@ -96,7 +105,8 @@ function noopEngine(): CalcEngine {
   return {
     update: () => [],
     rebuild: () => {},
-    value: () => null,
+    value: (_sheet, r, c) =>
+      r === 8 && c === 6 ? { error: "#DIV/0!", why: "0 으로 나눔(시험 칸 G9)" } : null,
     precedents: () => [],
     snapshot: () => ({}),
   };