PURPOSE: To obtain a self-excited type flyback converter which is improved in switching loss and switching noise by providing a circuit which delays conducting timing of a switching element control circuit to the circuit.

CONSTITUTION: Even when it is tried to supply a base current from winding N3 by inverting the voltage of each winding N1, N2, and N3, the conducting timing of a switching element SW is delayed due to a charge current to a capacitor C2. Therefore, the voltage drop of a capacitor CS produced due to the free vibration of the capacitor CS and winding N1 when the element SW is in a normal state approaches zero. As a result, the loss and noise generated when the electric charges in the capacitor CS are short-circuited by means of the element SW can be reduced. In other words, since the switching element SW is conducted in a state where the voltage shared by the element SW approaches zero, the loss and noise generated at the time of turning on can be reduced and this flyback converter can be reduced in noise, size, and weight and improved in efficiency.