To provide an inverter AC power supply capable of flexibly coping with complex switch control using a software program and also capable of coping with various requirements/specifications with a single configuration using a combination of a software and a fixed hardware of minimum scale.

Opening/closing control of the switch of an inverter arrangement is controlled with a program that runs on a processor such as a micro computer. So, a versatile AC power supply unit is realized which copes with different specifications with the same hardware by using a plurality of pieces of programs.