A laptop PC is enabled to operate with small power consumption while maintaining a specific function. A laptop PC is provided with a HDD and can operate in a normal mode and a doze mode as a new operating mode. In the doze mode, the computer can operate with power consumption less than in the normal mode while executing a process to implement a specific function. In the doze mode a shift event is created, and a process existing at that time is force-suspended or an I/O processing completion notification is suspended to a process that makes an I/O request to the HDD. As a result, the laptop PC is enabled to operate with small power consumption by stopping the HDD while maintaining a specific function.