An output shaft is arranged to be lateral and parallel to engine input shafts and a motor input shaft. An engine side gear mechanism for transmitting a power of the engine input shafts to the output shaft is provided. A motor side gear mechanism for transmitting a power of the motor input shaft to the output shaft is provided. An input side clutch engages and disengages the engine input shafts and the motor input shaft. When the input side clutch is engaged, the power transmission between a position where the engine side gear mechanism is arranged on the engine input shafts and a position where the motor side gear mechanism is arranged on the motor input shaft is invariably possible.