To prevent the breakage of a circuit by dissolving the stress to rush current suppression circuit.

The AC input voltage from an Ac power source 1 is supplied to the AC input end of a diode bridge 2, and the rectified voltage obtained at the rectified output end is supplied to a primary capacitor 3. The DC voltage filtered with this filter capacitor 3 is supplied to a DC-DC converter 3, and is converted into desired DC voltage, and this DC voltage is supplied to the circuit and the latter stage as the secondary input. Furthermore, one side of the neutral points of connection between the rectified output end of a diode bridge 2 and a filter capacitor 3 is provided with a rush current suppression circuit 5 consisting of an element such as a resistor, or the like so as to suppress the rush current. Together with it, this power unit is provided with a temperature detecting circuit 6 in close vicinity to this rush current suppressive circuit 5, and the output of this temperature detecting circuit 6 is supplied to a control circuit 7, and when the temperature of the rush current suppression circuit 5 comes to a specified value, the control to stop the oscillation of, for example, a DC-DC converter 4 is performed.