Hybrid drive system for a motor vehicle, including (a) an engine operated by combustion of a fuel, (b) a planetary gear mechanism having a sun gear and a carrier one of which is connected to the engine, and a ring gear connected to an output member, (c) a motor/generator connected to the output member, and (d) a differential gear device including output shafts and an input member rotated by a drive force received from the output member, and wherein the motor/generator, the planetary gear mechanism and the output member are arranged coaxially with each other along a first axis, and the output shafts of the differential gear device are disposed along a second axis parallel to the first axis. The planetary gear mechanism is disposed in a radially inner space provided radially inwardly of a stator coil of the motor/generator, and the input member includes a radially outer portion which overlaps a radially outer portion of the motor/generator in the radial direction of the motor/generator.