To provide a switching power supply which restrains increase in size and cost by reducing noise generated from diodes in the full-wave rectifying circuit and the switching circuit.

This switching power supply is provided with a full-wave rectifying circuit 4 for outputting a pulse using the diodes of which reverse recovery time is 1 μs or less for the diodes 471, 472 of which cathodes are connected to a wiring 47 used for the high-voltage side output of the pulse output, a smoothing capacitor 5 for providing a DC output by smoothing the pulse input from the full-wave rectifying circuit 4, a noise filter circuit 3 provided between the full-wave rectifying circuit 4 and the smoothing capacitor 5, to reduce noises generated with in the circuits of the successive stages and transferred to the AC input power supply side, and a switching circuit 6 for supplying a power required for the load by outputting the DC input from the smoothing capacitor 5 through the intermission, depending on the power requirement from the load.