To provide a DC power unit which is reduced in standby power consumption by reducing the number of components and, at the same time, does not consume excessive electric power at the time of supplying electric power.

The DC power unit is provided with a transformer 2, a switch 3 which switches the end section 21c of a primary winding and the tap 21b of a primary partral winding led out from the middle of the primary winding to each other, and a bridge rectifying means 4 which bridge-rectifies both- terminal outputs of a secondary winding. The power unit uses the both-terminal output of the bridge rectifying means 4 as a first DC output and the output based on the current between one output terminal of the means 4 and the tap 22b of a secondary partral winding as a second DC output, and, when the first DC output is supplied to a load 6 as power supply, the unit switches the input to the tap 21b by means of the switch 3. When no power supply is made to the load 6, the unit switches the input to the end section 21c of the primary winding by means of the switch 3.