PURPOSE: To turn off a power supply by a command from a microprocessor and to prevent entry data from damage due to malfunction of a power-off switch, by informing the operation of the power-off switch to the microprocessor by interruption.

CONSTITUTION: If the power-off switch 23 on a keyboard 21 is turned when power is supplied from a power supply controller to each component, an interruption request to the microprocessor 27 is generated by an output signal PWOF from the switch 23. By receiving the interruption request, the processor 27 generates, a signal PWOFC to command the off of the power supply to a power supply controller 24 during a period except data processing. By receiving the signal PWOFC, the controlling circuit 24 stops the power supply to components except an RAM 26, so that the entry data is prevented from damage due to malfunction of the switch 23.