AC module makers must prepare two types of AC modules for the 100-V and 200-V outputs only for domestic supply. For foreign countries, the makers must manufacture AC modules compatible with more system voltages. To solve these problems, the control circuit of an AC module controls the operation of an inverter circuit and/or the transformation ratio of a transforming circuit, and ON/OFF-controls a switch on the basis of the system voltage and connection state of an electric power system.