A differential speed change unit is installed in a housing at a position near an engine and arranged coaxial with a common axis, and a two-rotor type motor/generator unit is installed in the housing at a position away from the engine and arranged coaxial with the common axis. The motor/generator unit has inner and outer rotors and a wiring. An inner rotor shaft is connected with the inner rotor to rotate therewith. The inner rotor shaft extends coaxially with the common axis to be operatively connected to the differential speed change unit. An outer rotor shaft is connected with the outer rotor to rotate therewith. The outer rotor shaft extends coaxially with the common axis to be operatively connected to the differential speed change unit. The housing has a split section at which the housing is dividable into two housing parts, and the split section is positioned between the differential speed change unit and the motor/generator unit.