PURPOSE: To prevent bake loss accident or malfunction of an electronic device by providing a change-over switch as well as an output plug socket for each voltage system of AC100V and AC200V.

CONSTITUTION: The voltage of AC100V is converted into plural AC100V voltage systems and plural AC200V voltage systems by a power transformer 3, while each of change-over switches 9, 10 is connected respectively to plural taps for a group of the AC100V voltage systems and for a group of the AC200V voltage systems, so as to only one of these voltage systems is selected, and an output plug socket 4A of one AC100V system commonly used in the AC100V system, and an output plug socket 6A of one AC200V commonly used in the AC200V, are preferentially connected to each tap, through each of the change- over switches 9, 10. Voltage to be supplied to an electronic device can thus be constantly selected in the optimum manner.