PURPOSE: To simplify an internal circuit and to generate no radiation noise so as to prevent a bad influence from being given to the other circuit by providing a conversion element for converting input AC power into an optical output and solar batteries for receiving the optical output to convert it into DC power.

CONSTITUTION: AC input voltage is applied to input terminals 4a, 4b and converted into light by an electricity/light conversion element 2. Any of an electric bulb, fluorescent tube, light-emitting diode, etc., may be used as the electricity/light conversion element. Light, emitted from the electricity/light conversion element 2, is incident upon solar batteries 3 and converted into DC voltage. The desired DC voltage can be obtained by connecting in series the two or more solar batteries 3. The converted DC voltage is output to output terminals 5a, 5b.