To provide a high efficiency DC power circuit adjustable of output voltage for fluctuation of power receiving voltage, and to provide a high efficiency LED lighting system using the DC power with high LED luminescence quality.

A capacitor input type DC power circuit including a rectifier 6 connecting with an AC power supply 5 and a smoothing capacitor C1 connecting with the output of the rectifier 6 supplies power to the load 4 connecting with an output terminal. The DC power circuit disconnects the load 4 by a semiconductor switch MOS2 while the rectified voltage of the rectifier 6 exceeds the first predetermined value. During this period the DC power circuit is provided with: a first semiconductor switch SCR1 connecting with the smoothing capacitor C1 and the output terminal in the direction to discharge the electrical load of the smoothing capacitor C1 to the load; and an ignition circuit of the first semiconductor switch SCR1 that supplies a gate signal to the gate of the first semiconductor switch SCR1.