PURPOSE: To easily confirm the magnitude of a load current flowing to a power unit for guarding and, at the same time, to lower the output voltage of the power unit to 0V when an overcurrent is generated.

CONSTITUTION: A control circuit 15 detects the magnitude of a load current and turns on a load current indicator lamp 18 in accordance with the detected result. When an overcurrent is generated, the circuit 15 works upon a stabilization circuit 12 to lower the output voltage to 0V and, at the same time, turns on an overcurrent indicator lamp 19 and makes an abnormality alarm output terminal T2 to generate an output signal to the outside. Accordingly, the currently flowing load current can be recognized easily from the lamp 18 and whether or not an overcurrent is generated can be easily discriminated from the lamp 19. In addition, since the DC output is lowered to 0V when the overcurrent is generated, the fault of a power unit for guarding can be prevented. Moreover, the generation of the overcurrent can be easily detected from a place far from the installing place of the power unit for guarding by utilizing the output terminal T2.