An improved switching power supply which saves power when under a small to no load, wherein a transformer is provided comprising a primary winding to which a DC current is supplied by turning ON and OFF a switching device and a secondary winding for supplying an output signal to the load; an ON state control circuit turns ON the switching device by using the output signal induced at the secondary winding; an OFF state control circuit turns OFF the switching device using a current control signal obtained from the output signal from the secondary winding and a reference signal; and wherein a delay circuit prolongs the time at which the switching device makes the OFF to ON transition.