そもそも"-"を入力できないようにしました

frontend/src/pages/StockPage.tsx

@@ -350,6 +350,13 @@ const StockPage: React.FC = () => {
                   type="number"
                   value={editStock.amount}
                   onChange={handleChange}
+                  inputProps={{ min: 0 }}
+                  onKeyDown={(e) => {
+                    if (e.key === '-' || e.key === 'e' || e.key === 'E') {
+                      e.preventDefault();
+                    }
+                  }}
+
                 />
                 <TextField
                   label="購入価格"
@@ -359,6 +366,13 @@ const StockPage: React.FC = () => {
                   type="number"
                   value={editStock.price}
                   onChange={handleChange}
+                  inputProps={{ min: 0 }}
+                  onKeyDown={(e) => {
+                    if (e.key === '-' || e.key === 'e' || e.key === 'E') {
+                      e.preventDefault();
+                    }
+                  }}
+
                 />
                 {/* 購入日・消費期限を横並びに */}
                 <Box sx={{ display: 'flex', gap: 2, mb: 2 }}>