diff --git a/A00_Common/spreadsheet/spreadsheet_editor.ts b/A00_Common/spreadsheet/spreadsheet_editor.ts
index fc4de019..3ede2592 100644
--- a/A00_Common/spreadsheet/spreadsheet_editor.ts
+++ b/A00_Common/spreadsheet/spreadsheet_editor.ts
@@ -13,7 +13,7 @@ import { moveFormula } from "./spreadsheet_refshift";
 import { colName, parseA1, parseRange, rangeToA1, toA1 } from "./spreadsheet_address";
 import { funcHelp, suggestFunctions, type FuncHelp } from "./spreadsheet_func_help";
 import { defineName, resolveName } from "./spreadsheet_names";
-import { tokenize } from "./spreadsheet_parser";
+import { parseFormula, tokenize } from "./spreadsheet_parser";
 import { cellsOf, move, selectCell } from "./spreadsheet_selection";
 import { checkValue, findValidation } from "./spreadsheet_validation";
 import type { Cell, CellAddress, CellStyle, Sheet } from "./spreadsheet_types";
@@ -356,9 +356,19 @@ export function createEditor(ctx: SpreadsheetContext): Editor {
     focus();
   }
 
-  /** 칸에 적음 — 유효성(sub4) 「막음」 을 어기면 안 적고 false(편집 그대로 · 엑셀처럼 다시 치게) */
+  /** 칸에 적음 — 식이 틀렸거나(인자 수 등) 유효성(sub4) 「막음」 을 어기면 안 적고 false(편집 그대로 · 엑셀처럼 다시 치게) */
   function write(cells: CellAddress[], value: string, from: CellAddress): boolean {
     if (!st) return true;
+    const parsed = value.length > 1 && value[0] === "=" ? parseFormula(value) : null;
+    if (parsed && !parsed.ok) {
+      showToast(parsed.message, "error");
+      const node = src();
+      const at = Math.min(parsed.at + 1, node.value.length);
+      st.mode = "edit"; // 방향키가 글자 사이를 움직이게
+      st.point = null;
+      node.setSelectionRange(at, at);
+      return false;
+    }
     const sheet = sheetOf(st.sheet);
     const out: Record<string, Cell | null> = {};
     const warn = new Set<string>();