To provide a power circuit which can make a series regulator perform normal operation.

A power circuit 100 has a DC-DC converter 102 which converts the output voltage of a battery 200, a series regulator 104 which converts the output voltage of the DC-DC converter 102 and supplies it to a device 300, a bypass circuit 108 whose input end is connected between the battery 200 and the input end of the DC-DC converter 102 and whose output end is connected between the output side of the DC-DC converter and the input side of the series regulator 104, and a voltage detecting/detour control part 106 which detects the output voltage of the battery 200 andperforms the control of supplying the output voltage of the battery 200 directly to the series regulator 104, bypassing the DC-DC converter 102, by making a bypass circuit 108 conductive in case that this output voltage drops to a specified value or under, and also makes the bypass circuit 108 nonconductive after passage of a specified time since conduction.