AC power supply device 1 includes input capacitors 11 and 12 connected at a neutral point X of a three-phase output, transistor bridges 20* (where * denotes U, V, and/or W) each consisting of PWM control badges 20*1 and 20*2 each including two switch elements, transformers T* connected to output terminals of the transistor bridges 20*, reactors Ls* connected to the transformers T*, smoothing capacitors 40* connected to the reactors Ls*. The transformers T* are autotransformers including a core 33* and windings 31* and 32* coupled with each other via the core 33*. One ends of the windings are connected to output terminals of the PWM control bridges 20*1 and 20*2, respectively, while the other terminals are connected to the reactors Ls*. The windings 31* and 32* are wound in such directions that magnetic fluxes generated in the core 33* are cancelled with each other.