When a result of detection by a current sensor 22 represents the occurrence of an overcurrent, comparators 23 of PSUs 2 transmit a present report indicating that fact to an SP 1. Receiving the present report, an FPGA 12 of the SP 1 turns on a forcible low-power signal. A forcible power saving control circuit 32 of a CPU 3 directly inputs a forcible-low-power-mode signal, turns on the signal, and controls an instruction issuance control unit that is configured to issue an instruction in the CPU 3, so as to immediately decrease the frequency at which the instruction issuance control unit issues instructions. This control is cancelled after the DVFS control circuit 35 has reduced the voltage of power output from a DDC 4 and a clock frequency output from a PLL circuit.