A power converter (2; 2a) comprising: one or more first conversion circuits (10a, 10b) comprising a trench type transistor as a switching element (3a, 3b, 3c, 3d) for power conversion; one or more second conversion circuits (10c, 10d) comprising a planar type transistor as a switching element (3a, 3b, 3c, 3d) for power conversion; and a controller configured to select a conversion circuit to be operated according to an output command value for the power converter (2; 2a), wherein: all the one or more first conversion circuits (10a, 10b) are connected in parallel to said all the one or more second conversion circuits (10c, 10d), or all the one or more first conversion circuits (10a, 10b) are connected in series to said all the one or more second conversion circuits (10c, 10d); a principle structure of the trench type transistor as a switching element (3a, 3b, 3c, 3d) is the same as the principle structure of the planar type transistor as a switching element (3a, 3b, 3c, 3d), wherein the principle structure of the transistor is MOSFET, BJT, HFET, HEMT, JFET, IGBT, or RC-IGBT; and the controller is configured to stop all the one or more second conversion circuits (10c, 10d) and operate at least one of the one or more first conversion circuits (10a, 10b) while the output command value is lower than a predetermined output threshold value, and operate all the one or more first conversion circuits (10a, 10b) and operate at least one of the one or more second conversion circuits (10c, 10d) in a case where the output command value exceeds the predetermined output threshold value. one or more first conversion circuits (10a, 10b) comprising a trench type transistor as a switching element (3a, 3b, 3c, 3d) for power conversion; one or more second conversion circuits (10c, 10d) comprising a planar type transistor as a switching element (3a, 3b, 3c, 3d) for power conversion; and a controller configured to select a conversion circuit to be operated according to an output command value for the power converter (2; 2a), wherein: all the one or more first conversion circuits (10a, 10b) are connected in parallel to said all the one or more second conversion circuits (10c, 10d), or all the one or more first conversion circuits (10a, 10b) are connected in series to said all the one or more second conversion circuits (10c, 10d); a principle structure of the trench type transistor as a switching element (3a, 3b, 3c, 3d) is the same as the principle structure of the planar type transistor as a switching element (3a, 3b, 3c, 3d), wherein the principle structure of the transistor is MOSFET, BJT, HFET, HEMT, JFET, IGBT, or RC-IGBT; and the controller is configured to stop all the one or more second conversion circuits (10c, 10d) and operate at least one of the one or more first conversion circuits (10a, 10b) while the output command value is lower than a predetermined output threshold value, and operate all the one or more first conversion circuits (10a, 10b) and operate at least one of the one or more second conversion circuits (10c, 10d) in a case where the output command value exceeds the predetermined output threshold value. all the one or more first conversion circuits (10a, 10b) are connected in parallel to said all the one or more second conversion circuits (10c, 10d), or all the one or more first conversion circuits (10a, 10b) are connected in series to said all the one or more second conversion circuits (10c, 10d); a principle structure of the trench type transistor as a switching element (3a, 3b, 3c, 3d) is the same as the principle structure of the planar type transistor as a switching element (3a, 3b, 3c, 3d), wherein the principle structure of the transistor is MOSFET, BJT, HFET, HEMT, JFET, IGBT, or RC-IGBT; and the controller is configured to stop all the one or more second conversion circuits (10c, 10d) and operate at least one of the one or more first conversion circuits (10a, 10b) while the output command value is lower than a predetermined output threshold value, and operate all the one or more first conversion circuits (10a, 10b) and operate at least one of the one or more second conversion circuits (10c, 10d) in a case where the output command value exceeds the predetermined output threshold value. stop all the one or more second conversion circuits (10c, 10d) and operate at least one of the one or more first conversion circuits (10a, 10b) while the output command value is lower than a predetermined output threshold value, and operate all the one or more first conversion circuits (10a, 10b) and operate at least one of the one or more second conversion circuits (10c, 10d) in a case where the output command value exceeds the predetermined output threshold value.