Circuit for battery/capacitor power source

A power circuit includes a linear voltage control block 5 for stepping down a charged voltage of a power assist capacitor to a predetermined voltage value within an operating voltage range of a load when an output voltage of a power supply in the form of a battery 2 exceeds an upper limit value of the operating voltage range of the load, and for controlling the charged voltage of the power assist capacitor to a voltage value substantially equal to the output voltage of the power supply when the output voltage of the power supply falls within the operating voltage range of the load, and a current control block 6 for controlling an upper limit value of the output current of the power supply using a predetermined current value in a power range necessary for operating the load.