PURPOSE: To improve reliability by adding control routine to check the set value of a counter for controlling timer interruption at every occurrence of the timer interruption, and decide whether a power auto-off function is to be executed or not according to the set value.

CONSTITUTION: When the timer interruption is generated by a PIC 2, in timer routine, control is executed on all such occasions in conformity to a flow chart shown in another figure. Namely, at first, the set value of the counter for con trolling the timer interruption built in a PIT 3 is checked [step (a)]. If the set value is less than some value (e.g., 50 ms), power auto-off control routine comes to an end without being executed. If the set value is more than some value, the power auto-off control routine is executed [step (b)]. In this power auto-off control routine, it is checked whether a counted value reaches the value set beforehand or not in addition to the count-up and the clear of the counter for power auto-off, and if it reaches the set value, an OFF command is issued to a power supply controller 8 and an HDD device 5, etc.