NOVELTY - The apparatus (2) has two switching units (S1, S2) placed between a direct current (DC) power supply (10) and a primary side of an isolation transformer (T). A series circuit includes a load (16) and an inductor (L) connected in series with each other, and is placed on a secondary side of the transformer. A third switching unit (S4) is placed between the circuit and the secondary side, where the apparatus sends out power from the supply toward the load as DC power or alternating current (AC) power of an arbitrary polarity, or regenerates and supplies the power from the load to the supply.    USE - Isolated power conversion apparatus for use as an emergency power supply to charge a battery of a plug-in hybrid car and electric car, a power consumption leveling apparatus with a power storage device for commercial power supply, and grid connection inverter or power conditioner for wind power generation, fuel cell power generation, and solar power generation. Uses include but are not limited to isolated bipolar bidirectional DC/DC converter, isolated bidirectional DC/AC inverter, dual-output DC/DC converter, and triple-output DC/DC converter.    ADVANTAGE - The apparatus can achieve positive output and negative output and regenerate output-side DC power to a DC power supply without additional configuration when the apparatus is used as an isolated DC/DC converter. The apparatus can output AC power by causing the isolated DC/DC converter to continuously change positive/negative output when the apparatus is used as an isolated DC/AC inverter, and requires fewer bidirectional switching elements such that the DC/AC inverter has simpler configuration, smaller size, and less weight, and requires lower cost. The apparatus utilizes readily acquirable unidirectional switching elements as switching units on the secondary side so as to reduce cost of the apparatus. The apparatus can operate as the isolated DC/DC converter or as the isolated DC/AC inverter without changing configuration of the apparatus. The apparatus utilizes a full-bridge type circuit to improve utilization efficiency of a primary coil of the transformer higher than that of a push-pull type so as to reduce an occupation rate of a primary coil, thus enabling miniaturization of the transformer.    DETAILED DESCRIPTION - The switching units are selected from a group consisting of MOSFET, junction FET (J-FET), bipolar transistor, insulated gate bipolar transistor (IGBT), and bidirectional switching element.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of an isolated power conversion apparatus.    Inductor (L)    Switching units (S1-S3, S3', S4, S4')    Isolation transformer (T)    Isolated power conversion apparatus (2)    Power supply (10)    Load (16)