An SCP (System Control Processor) 7 is provided in addition to a CPU 1 responsible for control of circuits in a computer. Upon receiving a Main ON signal (low level) indicative of the CPU 1 being inactive, the SCP 7 responds to a switch operation on a control panel 6 to supply a CD-ROM drive 2 with a command corresponding to the switch operation on said control panel 6 independently of the CPU 1 as well as to feed a high-level CD-POWER-ON signal to a power supply circuit 8 through an OR circuit 9. The power supply circuit 8 selectively supplies the CD-ROM drive 2 and an Audio amplifier 10 with driving power upon receiving the high-level signal.