To provide a power source which suppresses higher harmonic currents and is high in a power factor.

In a switching power source where AC voltage is inputted, a controllable switch element 15 is provided between a primary rectifying circuit 1 and a switching circuit 3, and the switch element 15 controls the discharging of the capacitor 11 charged with the voltage obtained from a transformer 8, according to the voltage change of the terminal voltage of the capacitor. Therefore, this power source can have the effect of suppressing the input higher harmonic wave current and the effect of securing the output stability at an instantaneous stoppage.