A power supplying power supply circuit which supplies power to an N-phase PWM control DC/DC converter power supply circuit multiplies the output voltage thereof by 1/N by use of a voltage divider and outputs the result of multiplication to the inverting input terminal of an error amplifier. Further, the power supplying power supply circuit inputs the output voltage of the N-phase PWM control DC/DC converter power supply circuit to the non-inverting input terminal via a switching circuit. An output of the error amplifier is supplied to a transistor so as to control and set the voltage value of output power of the power supplying power supply circuit equal to N.times.output voltage of the N-phase PWM control DC/DC converter power supply circuit.