In a standby mode, a voltage step up DC/DC converter 5 supplies a power output voltage equal to or higher than a second set voltage which is lower than a first set voltage in a normal operating mode to a microcomputer (load) 1 with current supply performance which is smaller than in the normal operating mode. On the other hand, in the normal operating mode, a voltage step up/step down DC/DC converter 4 supplies the first set voltage in the normal operating mode to the microcomputer 1.