Abstract: A switching regulator which is designed so that a negative feedback is applied to the base of a transistor constituting an oscillator adapted for chopping a DC voltage, only during a period of time which is required to effect pulse width control when the transistor is switched from conduction to non-conduction. A control circuit may also be provided which is arranged to compare the output of a current detecting circuit for detecting a current proportional to a current for driving a transformer with the output of an error voltage amplifier for amplifying an output resulting from comparison of a rectified version of the AC output of the transformer with a reference voltage. The foregoing control circuit is also arranged so that when the output of the current detecting circuit exceeds the output of the error voltage amplifier, a trigger signal is imparted to cause the oscillator to be changed from the on state to the off state.