A DC power circuit comprises a first control means which is provided between a DC power source and a pair of output terminals for controlling voltages as well as currents supplied to a load from the DC power source. An output current detector detects the output current from the DC power source, and provides a first control potential proportional to the detected current. On the other hand, an output voltage detector is coupled between the pair of output terminals for detecting the voltage applied to the load, and provides a second control potential proportional to the detected voltage. A second control means selectively assumes one of two stable states in response to external control. A third control means receives the first and second control potentials, and responds to the state of the second control means for controlling the first control means based on the received two control potentials.