To reduce power loss in a switching power supply and supply power to a switching control circuit with stability all the time regardless of the level of output voltage.

The control power circuit (12) of the switching power supply is provided with an accumulating circuit (22) that is charged at startup with a current flowing from a direct-current power supply (1) to primary winding (2a) and a main switching element (3), a comparing means (23) that produces an output signal when the charging voltage (VC1) of the accumulating circuit (22) reaches a starting reference voltage level (V1) and stops the output signal when the voltage (VC1) of the accumulating circuit (22) drops to a stopping reference voltage level (V2) lower than the starting reference voltage level (V1), and an auxiliary switching element (24) that is connected in series with the main switching element (3) and is brought into on-state on an output signal from the comparing means (23). Even if the output voltage fluctuates, the accumulating circuit (22) supplies the control circuit (10) with power for driving having a certain charging voltage (VC2) after the auxiliary switching element (24) is switched to on-state.