A device comprising: a reverse conducting semiconductor device including an IGBT element domain and a diode element domain coexisting in a mutual semiconductor substrate, wherein a first conductive type drift region and a second conductive type body region extend evenly within both the IGBT element domain and the diode element domain, in the IGBT element domain, the second conductive type body region, the first conductive type drift region, and a second conductive type collector region are laminated, a first conductive type emitter region is formed on a surface of the body region, and a first trench gate electrode penetrating the body region that separates the emitter region from the drift region is formed, in the diode element domain, the second conductive type body region, the first conductive type drift region and a first conductive type drift contact region are laminated, a first conductive type first body contact region and a second conductive type second body contact region are formed on a surface of the body region, and a second trench gate electrode penetrating the body region that separates the first body contact region from the drift region is formed facing the first trench gate electrode; characterized in that a first gate voltage applying circuit is electrically connected to the first trench gate electrode for controlling a voltage applied to the first trench gate electrode; and a second gate voltage applying circuit is electrically connected to the second trench gate electrode for controlling a voltage applied to the second trench gate electrode, wherein each of the first and second gate voltage applying circuits (10, 12) is configured so as to apply a first voltage to at least the first trench gate electrode in a case where the IGBT element domain is maintained in an on-state, and a second voltage to at least the second trench gate electrode in a case where return current flows in the diode element domain, when the first voltage is higher than that of the body region, then the second voltage is higher than that of the body region, and when the first voltage is lower than that of the body region, then the second voltage is lower than that of the body region, and the first and second gate voltage applying circuits are composed by one single gate voltage applying circuit. a reverse conducting semiconductor device including an IGBT element domain and a diode element domain coexisting in a mutual semiconductor substrate, wherein a first conductive type drift region and a second conductive type body region extend evenly within both the IGBT element domain and the diode element domain, in the IGBT element domain, the second conductive type body region, the first conductive type drift region, and a second conductive type collector region are laminated, a first conductive type emitter region is formed on a surface of the body region, and a first trench gate electrode penetrating the body region that separates the emitter region from the drift region is formed, in the diode element domain, the second conductive type body region, the first conductive type drift region and a first conductive type drift contact region are laminated, a first conductive type first body contact region and a second conductive type second body contact region are formed on a surface of the body region, and a second trench gate electrode penetrating the body region that separates the first body contact region from the drift region is formed facing the first trench gate electrode; characterized in that a first gate voltage applying circuit is electrically connected to the first trench gate electrode for controlling a voltage applied to the first trench gate electrode; and a second gate voltage applying circuit is electrically connected to the second trench gate electrode for controlling a voltage applied to the second trench gate electrode, wherein each of the first and second gate voltage applying circuits (10, 12) is configured so as to apply a first voltage to at least the first trench gate electrode in a case where the IGBT element domain is maintained in an on-state, and a second voltage to at least the second trench gate electrode in a case where return current flows in the diode element domain, when the first voltage is higher than that of the body region, then the second voltage is higher than that of the body region, and when the first voltage is lower than that of the body region, then the second voltage is lower than that of the body region, and the first and second gate voltage applying circuits are composed by one single gate voltage applying circuit.