To reduce a current consumption caused by keep on depressing an operation key for a long time in a portable apparatus.

A control switch 3 and an operation switch 1 are connected in series to a power supply voltage. In an initial state, a control switch is in an ON-state. Therefore, if the operation switch is pressed down, a logic H is obtained and the press-down of the operation switch is detected. When it is detected, the control switch is turned off. After a predetermined lapse of time, the control switch is once turned on and, at that time, it is detected whether the operation switch is depressed or not. In the operation switch is kept in the on-state, the control switch is turned off again and turned on after a predetermined lapse of time and a process for detecting the depression of the operation switch is repeated.