There is provided a self-excited switching power supply circuit which shifts to continuous oscillating operation immediately after the self-excited switching power supply circuit is connected to an AC power supply and started and which does not cause start-up failure while using a start-up resistor of a high resistance value to maintain standby power consumption at a low level. A bypass charging circuit connected in series to a start-up resistor is connected between a high-voltage side terminal of a DC input power supply and the gate of an oscillation field effect transistor. A charging current flowing in the start-up resistor, and additionally, a charging current to charge a start-up capacitor through the bypass charging circuit flow in a transitional period during which the voltage of the DC input power supply increases.