To provide a computer system of low electric power consumption.

This computer system 1 is provided with a PC 10, a protocol converting part 20, a drive 30, a packet selecting part 40, a cable condition detecting part 50 arid a drive control part 60. The packet selecting part 40 transmits a detection signal to the drive control part 60, when detecting a packet including a wake-up command for bringing the drive 30 into an active condition out of packets transmitted to from the PC 10 to the protocol converting part 20. The cable condition detecting part 50 detects whether a cable between the PC 10 and the protocol converting part 20 is under a connected condition or not, and transmits a detected result to the drive control part 60 by a signal. The control part 60 issues the wake-up command or a sleep command to the protocol converting part 20 when receiving the detection signal from the packet selecting part 40 or the cable condition detecting part 50, and allows or stops the transmission of a protocol-converted command and data to the drive 30.