Excel のグラフで日付が数値（軸上のシリアル値）になる

Tested in: The serial, TEXT, and DATEVALUE results below were evaluated in Google Sheets on 12 November 2026. Excel 365 menu names are the current desktop labels; I did not click through Format Axis in Excel this session.

How to pick a line vs a column chart is in How to Make a Chart in Excel. This page is only about an axis that shows serials.

The number is the date

Excel and Google Sheets store a date as a whole number of days from a fixed origin. In the test workbook:

=DATE(2024,1,8)
=TEXT(DATE(2024,1,8),"yyyy-mm-dd")

The first formula is serial 45299 (that is what you see if the cell or the axis is formatted as a number). The second returned 2024-01-08. Nothing is “wrong” with 45299 except the format.

In Excel 365

1. Click the chart, then right-click the horizontal axis.
2. Choose Format Axis.
3. Open the Number section (sometimes under Axis Options).
4. Set the category to Date, or type a format code such as yyyy-mm-dd or d-mmm.
5. If the axis still shows 1, 2, 3, the chart is not using your date column as the category. Open Select Data and set the horizontal (category) labels to the date range.

In Google Sheets

1. Click the chart, then open the chart editor.
2. Under Customize > Horizontal axis, set a date number format if the option is there.
3. If it is not, format the source date column as a date (Format > Number > Date) and, in Setup, confirm the date column is the X-axis.

When the source is text, not a serial

Formatting the axis does not fix labels that were typed as text. A cell can look like 2024-01-08 and still be text. In the test workbook I stored those characters as text in L4:

=ISTEXT(L4)
=ISNUMBER(L4)
=DATEVALUE(L4)

On 12 November 2026 those returned TRUE, FALSE, and 45299. DATEVALUE produced the same serial as =DATE(2024,1,8). Put that converted column on the axis, or paste the values over the text, then format the axis as a date.

If DATEVALUE returns #VALUE!, the text is not in a date order your locale expects. Use the conversions in dates stored as text. Mixed columns — some real dates, some text — produce an axis that looks partly numbered, partly labeled, and a line chart that treats the labels as unordered categories.

The axis used the wrong column

A second common cause is a chart built from the value column only. Excel then uses 1, 2, 3 as the axis, or it plots the dates as a second series of large numbers (45299 sits far above a revenue series of 7800). In Select Data, the date column should be the category axis, and the revenue (or quantity) column should be the series. Do not include both the date serial and the revenue as two series on the same value axis.

A pivot chart can show serials for the same reason: the date field is a number, and the chart inherited a General format. Format the axis, or group the pivot dates first so the axis shows month labels. If Group is disabled, fix the source as in cannot group dates in a pivot table.

Once the axis shows 8 Jan 2024 instead of 45299, check that the points are in date order. Text labels sort alphabetically; real dates sort as numbers, which is what you want on a time scale.