A switching power supply apparatus comprising: a first transformer, one end of a primary winding thereof being connected to one end of a secondary winding of a converter transformer; a second transformer, one end of a primary winding thereof being connected to another end of the secondary winding of the converter transformer; a reactor connected to both ends of a series circuit having the secondary windings; a smoothing capacitor, one end thereof being connected to the primary windings of transformers; a first diode connected to a connection between the first winding and a second winding of the first transformer and the other end of the smoothing capacitor; and a second diode connected to a connection between a first winding and a second winding of the second transformer and the other end of the smoothing capacitor.