PURPOSE: To realize not only the processing of words, but the airthmetic processing of a numeral, by inputting the arithmetic result of an arithmetic means at any position in any writings.

CONSTITUTION: When input data is supplied from a keyboard KBD to a microprocessor MPU, the MPU discriminates what kind of key the data is inputted by using a microprogram stored in an ROM. When it is judged that the input data is fed from an arithmetic start key, echo back processing is started. When it is judged that the input data is fed from a total key, on the other hand, the contents of an arithmetic start flag are discriminated and when the flag is on, calculation processing is performed on the basis of arithmetic data inputted so far to output the result to a display device CRT. Thus, the arithmetic result is outputted at any position on the CRT screen, so the arithmetic processing of the numeral is possible.