PURPOSE: To prevent erroneous input by incorporating the function of displaying previously inputted numerical value and arithmetic key when numerical values are inputted into a calculator.

CONSTITUTION: An instruction input part 7 is given numerical values from a numerical value inputting part 3 for inputting numerical values and operators from an operator inputting part 4 for inputting operators, and a process instructing part 8 interprets a request instructed by the instruction input part 7, and starts respective processes, and a calculation processing part 9 executes calculations based upon calculation instructions from the process instructing part 8. A numerical value storing part 10 stores the inputted numerical values based upon the instruction from the process instructing part 8, and then outputs the stored numerical values to the process instructing part 8. Further, an operator storing part 11 stores inputted operators based upon the instruction from the process instructing part 8 and outputs the stored operators to the process instructing part 8. Then, a data display part 6 displays numerical values on a numerical value display part 1 or displays operators on an operator display part 2 based upon the instruction of the process instructing part 8.