To provide a transformer device which can convert different AC voltages to a desired voltage and can be made compact in size and light in weight.

The transformer device includes a primary winding (3) for receiving an AC voltage, a plurality of secondary windings (4a, 4b) having different coil turn numbers, and a voltage conversion circuit (5) for converting AC voltages induced in the plurality of secondary windings (4a, 4b). Each of the plurality of secondary windings (4a, 4b) has first and second terminals not fixed in potential. The first and second terminal are provided for each of the secondary windings (4a, 4b). The transformer device further includes a switch circuit (8) for selectively connecting the first and second terminals of each of the secondary windings (4a, 4b) to the voltage conversion circuit (5).