To enable output voltage control excellent in precision, while reducing power loss for light load, and to carry out sure starting in a self-excited oscillation type power converter.

A power converter performs self-excited oscillation by a transformer 2, having windings 24, 25 for driving semiconductor switch elements 71, 72. When a load current detected by a detection circuit 131 or a current value corresponding to the load current is at most a prescribed value, intermittent driving pulses are generated from a pulse-generating circuit 141, and the semiconductor switch 71 is driven intermittently. In accordance with the deviation of an output voltage from a set value Vo, the width of the intermittent driving pulses is changed by an output voltage detection adjusting circuit 121. Thereby jumping of the output voltage when the load is light is prevented, and starting at heavy-load time is enabled sufficiently.