The present invention realized miniaturization of a power supply device using a multiphase system. The power supply device includes, for example, a common control unit, a plurality of PWM-equipped drive units, and a plurality of inductors. The common control unit outputs clock signals respectively different in phase to the PWM-equipped drive units. The clock signals are controllable in voltage state individually respectively. For example, the clock signal can be brought to a high impedance state. In this case, the PWM-equipped drive unit detects this high impedance state and stops its own operation. It is thus possible to set the number of phases in multiphase arbitrarily without using another enable signal or the like.