A method for driving a power supply device including a plurality of reverse conducting semiconductor devices (10a-10d) used in combination, wherein: each reverse conducting semiconductor device (10a-10d) includes an IGBT (insulated gate bipolar transistor) domain and a diode element domain coexisting in a semiconductor substrate, in the IGBT domain, an emitter region, a body region, a drift region and a collector region are layer-stacked, and a trench gate electrode penetrating the body region that separates the emitter region from the drift region is formed, in the diode element domain, a body contact region, a body region, a drift region and a drift contact region are layer-stacked and a trench gate electrode extending from a surface of the semiconductor substrate to the drift region is formed, the body region and the drift region are common for the IGBT domain and for the diode element domain and two trench gate electrodes connected and opposite to each other are formed respectively in the IGBT domain and the diode element domain, the power supply device comprises a parallel circuit comprised of a plurality of series circuits (12a, 12b) connected in parallel, wherein each of the plurality of series circuits (12a, 12b) includes two reverse conducting semiconductor devices connected in series, the parallel circuit is connected between a first terminal of the power source and a low electric potential second terminal and intermediate electric potential points (14a, 14b) each between the two reverse conducting semiconductor devices in each of the plurality of series circuits (12a, 12b) are connected to a load, characterized in that the driving method comprises: applying a first polarity voltage at least to the trench gate electrode of the IGBT domain of one reverse conducting semiconductor device such that an electric power is supplied to the load and that the IGBT domain of the one reverse conducting semiconductor device is switched to an on-state; and applying a second opposite polarity voltage at least to the trench gate electrode of the diode element domain of the other reverse conducting semiconductor device which is present in the same series circuit when the IGBT domain of the one reverse conducting semiconductor device is switched to an off-state and thus the return current flows in the diode element domain of the other reverse conducting semiconductor device each reverse conducting semiconductor device (10a-10d) includes an IGBT (insulated gate bipolar transistor) domain and a diode element domain coexisting in a semiconductor substrate, in the IGBT domain, an emitter region, a body region, a drift region and a collector region are layer-stacked, and a trench gate electrode penetrating the body region that separates the emitter region from the drift region is formed, in the diode element domain, a body contact region, a body region, a drift region and a drift contact region are layer-stacked and a trench gate electrode extending from a surface of the semiconductor substrate to the drift region is formed, the body region and the drift region are common for the IGBT domain and for the diode element domain and two trench gate electrodes connected and opposite to each other are formed respectively in the IGBT domain and the diode element domain, the power supply device comprises a parallel circuit comprised of a plurality of series circuits (12a, 12b) connected in parallel, wherein each of the plurality of series circuits (12a, 12b) includes two reverse conducting semiconductor devices connected in series, the parallel circuit is connected between a first terminal of the power source and a low electric potential second terminal and intermediate electric potential points (14a, 14b) each between the two reverse conducting semiconductor devices in each of the plurality of series circuits (12a, 12b) are connected to a load, characterized in that the driving method comprises: applying a first polarity voltage at least to the trench gate electrode of the IGBT domain of one reverse conducting semiconductor device such that an electric power is supplied to the load and that the IGBT domain of the one reverse conducting semiconductor device is switched to an on-state; and applying a second opposite polarity voltage at least to the trench gate electrode of the diode element domain of the other reverse conducting semiconductor device which is present in the same series circuit when the IGBT domain of the one reverse conducting semiconductor device is switched to an off-state and thus the return current flows in the diode element domain of the other reverse conducting semiconductor device applying a first polarity voltage at least to the trench gate electrode of the IGBT domain of one reverse conducting semiconductor device such that an electric power is supplied to the load and that the IGBT domain of the one reverse conducting semiconductor device is switched to an on-state; and applying a second opposite polarity voltage at least to the trench gate electrode of the diode element domain of the other reverse conducting semiconductor device which is present in the same series circuit when the IGBT domain of the one reverse conducting semiconductor device is switched to an off-state and thus the return current flows in the diode element domain of the other reverse conducting semiconductor device