A switching power supply apparatus is provided with a switching circuit and an even number of transformers. The transformer are provided with: cores each having an identical shape; primary windings each having an identical arrangement around the cores, and each having first and second terminals; and secondary windings each having an identical arrangement around the cores, and each having third and fourth terminals. The primary windings of the transformers are connected so that when a current flows from the first terminal to the second terminal of a first transformer, a current flows from the second terminal to the first terminal of a second transformer. The secondary windings of the transformers are connected so that when a current flows from the third terminal to the fourth terminal of the first transformer, a current flows from the fourth terminal to the third terminal of the second transformer.