In response to an external interrupt signal input from a disk eject button 5 to an external interrupt port 2, a control unit 14 wakes up from a sleep mode and shifts to a regular operation mode. A wakeup counter 15 measures the number of times of wakeups. If the number of times of the wakeups reaches a predetermined number of times, an interrupt control unit 11 disables the external interrupt to the external interrupt port 2, and ignores the external interrupt signal thereafter, and the control unit 14 forcefully shifts from the regular operation mode to the sleep mode.