PURPOSE: To prevent misconversion and improve customer service by providing a display data arithmetic means and processing and displaying display data from an information equipment in addition to its display.

CONSTITUTION: The display data which is inputted from an interface part 20 is inputted to a display control circuit 11 and converted here into display unit drive information, which is displayed on the 1st line of a display unit 12. At the same time, an arithmetic circuit 111 adds the data to last input data and the sum data is displayed on the 2nd line of the display unit 12. Then when display data is inputted next, this data is displayed rewriting the 1st line of the display unit 12. Then the display data and sum data are added together and their addition data is displayed on the 2nd line of the display unit 12. Every time display data is inputted, the display data and sum data are displayed on the 1st and 2nd lines of the display unit.