A power control circuit includes a switching regulator for converting voltage of external electric power into a medium voltage, a series regulator for converting the medium voltage to a prescribed voltage of output power to be supplied and a circuit for operating either the switching regulator or the series regulator under a protective condition if overvoltage or overcurrent is detected. The switching regulator includes a first transistor, a smoothing circuit and a first control circuit for controlling switching operation of the first transistor. The series regulator includes a second transistor and a second control circuit for controlling conductivity of the second transistor to regulate voltage of the output power to be constant, an overvoltage detecting circuit for detecting an overvoltage of the medium voltage, and an overcurrent detecting circuit for detecting an overcurrent supplied to the series regulator.