PURPOSE: To enable a handy arithmetic unit to be similarly used by right-handed and left-handed users.

CONSTITUTION: The handy arithmetic unit 100 has buttons 314, 316 and 318 symmetrically arranged on one side so as to easily operate left-hand holding or right-hand holding due to the holding hand. The handy arithmetic unit 100 is provided with a constituting method so that the directions of images on the button function and a display screen can be made adaptive for the left-hand or right-hand holding operation of the arithmetic unit. The input of a stylus 304 is changed by button pressing and corresponding to input information to the arithmetic unit, flexibility is applied. Concerning this arithmetic unit, the buttons have roundness 332 so that an operator can easily utilize the unit.