A hybrid drive system includes an input shaft of an automatic transmission, a clutch, an intermediate shaft, and a first gear disposed on a first shaft coaxial with an engine output shaft. An electric motor and a second gear provided on an output shaft of the electric motor are disposed on a second shaft. A rotation of the engine output shaft is transmitted to the input shaft through the clutch and the intermediate shaft, and a rotation of the electric motor is transmitted to the input shaft through the second gear and the first gear. The intermediate shaft is supported by a first support wall through a bearing. The clutch is disposed between the intermediate shaft and the engine output shaft, and a front side of the input shaft is rotatably supported by a second support wall, and connected to a rear side of the intermediate shaft through a spline.