PURPOSE: To reduce the cost of an apparatus and to miniaturize the apparatus by supplying a load with a superposed voltage of the output voltages of a flyback circuit and a chopper circuit.

CONSTITUTION: A DC output voltage E1 supplied to the load RL1 of a flyback circuit A1 is E1E2+EA1, and an energy shared to a transformer T1 and a transistor Q11 out of an energy given to the load RL1 is not more than that corresponding to a DC output voltage EA1. Therefore, a transistor current i11 becomes smaller and a power transistor Q11 may be of a small capacity. On the other hand, an energy corresponding to the DC output voltage E2 is shared to a transistor Q21 and a smoothing reactor L21 of a chopper circuit B. The current i21 of the transistor Q21 is i21iO+iL and flows as a square- wave current equivalent to a load current iL. Consequently, the current is not a triangular-wave current as in the case of the flyback circuit A1, and a transistor with a low rated power may be used as the power transistor Q21.