PURPOSE: To prevent the deterioration in the appearance of a display screen owing to the overlap of data by changing the form of display while the whole number of digits of data is viewed.

CONSTITUTION: When there is no correction of data, code data is inputted from a data input means 1, and the code is displayed in the display area 4a of a display means 4. When an execution key is operated after code data is inputted, display data corresponding to the inputted code is read from a display data storage means 2 and is displayed on the display area 4a instead of a code which does not require display. When there is a correction instruction by a correction instruction means 3, and input data inputted as the object of correction is not overlapped with display data on the display area 4a, input data and said display data are both displayed. When input data inputted as the object of correction overlaps with inputted input data on the display area 4a, only input data is displayed. Consequently, the display of display data can be changed in accordance with displayed data.