To improve the learning effect of a user by enabling evaluation on whether the unit of a solution in a calculation formula is a correct physical unit.

An arithmetic unit is equipped with: a storage 13 for storing an appropriate unit table 71 for storing a prescribed unit as an appropriate unit; a display part 15 for displaying the calculation formula where a numerical value or character with the unit is defined as a component; a CPU 11 for acquiring the solution of the calculation formula displayed in the display part 15 by an operation; and the display part 15 for displaying the effect that the unit of the solution in the calculation formula acquired by the CPU 11 does not agree with any appropriate units stored in the appropriate unit table 71 when the agreement is not obtained.