A first motor/generator unit (10A comprises a first rotor (42) and a first stator (40) with a plurality of coils. A second motor/generator unit (10B) comprises a second rotor (43) and a second stator (41) with a plurality of coils. By properly determining the number of coils S1, S2 in the stators (40, 41), the number of pairs of magnetic poles P1, P2 in the magnet of the rotors (42, 43), and the number of phases M1, M2 in alternating currents driving the rotors (42, 43), and connecting a coil with a coil number j in a group number i of the first stator (40) with a coil with a coil number i in a group number j of the second stator (41), it is possible to suppress an ineffectual current generated when two motor/generator units (10A, 10B) are independently driven by the same inverter (32).