A hybrid vehicle comprising: an engine comprising a cylinder and a crankshaft; a drive motor comprising a motor housing (Ma) and a motor drive shaft (Mb) projecting laterally from the motor housing (Ma); a transmission comprising an input shaft, an output shaft, and a gear train, the transmission being configured to change the speed of rotation produced by rotational power transmitted from the engine and the drive motor to the input shaft and output the resulting rotation to a drive wheel; a main clutch connected to one end of the input shaft of the transmission and disposed in a power transmission route between the crankshaft (Ea) of the engine and the input shaft of the transmission; a crankcase accommodating the crankshaft (Ea), the input shaft, the output shaft, the gear train, and the main clutch; and a power transmission mechanism that transmits power from the motor drive shaft (Mb) to the input shaft, wherein the crankcase comprises a main body portion aligned with the drive motor in a direction perpendicular to the motor drive shaft (Mb), the power transmission mechanism is located partly in a first region defined by the main body portion, the crankcase comprises a case body and a cover (28, 29) removably mounted on the case body, a main chamber accommodating at least the crankshaft (Ea), the input shaft, the output shaft, and the gear train is formed in the case body, a subsidiary chamber accommodating at least the main clutch is formed between the case body and the cover, and the first region is located in the subsidiary chamber, characterized in that: the crankcase comprises an extended portion continuous with the main body portion and located lateral to the motor housing (Ma), the extended portion receiving insertion of one end of the motor drive shaft (Mb), the power transmission mechanism is located partly in a second region defined by the extended portion and communicating with the first region, wherein the second region is located in the subsidiary chamber, and the cover (28, 29) comprises a portion covering the first region from outside in a vehicle width direction of the hybrid vehicle and a portion covering the second region from outside in the vehicle width direction, the portion covering the second region being located inwardly of the portion covering the first region in the vehicle width direction. an engine comprising a cylinder and a crankshaft; a drive motor comprising a motor housing (Ma) and a motor drive shaft (Mb) projecting laterally from the motor housing (Ma); a transmission comprising an input shaft, an output shaft, and a gear train, the transmission being configured to change the speed of rotation produced by rotational power transmitted from the engine and the drive motor to the input shaft and output the resulting rotation to a drive wheel; a main clutch connected to one end of the input shaft of the transmission and disposed in a power transmission route between the crankshaft (Ea) of the engine and the input shaft of the transmission; a crankcase accommodating the crankshaft (Ea), the input shaft, the output shaft, the gear train, and the main clutch; and a power transmission mechanism that transmits power from the motor drive shaft (Mb) to the input shaft, wherein the crankcase comprises a main body portion aligned with the drive motor in a direction perpendicular to the motor drive shaft (Mb), the power transmission mechanism is located partly in a first region defined by the main body portion, the crankcase comprises a case body and a cover (28, 29) removably mounted on the case body, a main chamber accommodating at least the crankshaft (Ea), the input shaft, the output shaft, and the gear train is formed in the case body, a subsidiary chamber accommodating at least the main clutch is formed between the case body and the cover, and the first region is located in the subsidiary chamber, characterized in that: the crankcase comprises an extended portion continuous with the main body portion and located lateral to the motor housing (Ma), the extended portion receiving insertion of one end of the motor drive shaft (Mb), the power transmission mechanism is located partly in a second region defined by the extended portion and communicating with the first region, wherein the second region is located in the subsidiary chamber, and the cover (28, 29) comprises a portion covering the first region from outside in a vehicle width direction of the hybrid vehicle and a portion covering the second region from outside in the vehicle width direction, the portion covering the second region being located inwardly of the portion covering the first region in the vehicle width direction. the crankcase comprises an extended portion continuous with the main body portion and located lateral to the motor housing (Ma), the extended portion receiving insertion of one end of the motor drive shaft (Mb), the power transmission mechanism is located partly in a second region defined by the extended portion and communicating with the first region, wherein the second region is located in the subsidiary chamber, and the cover (28, 29) comprises a portion covering the first region from outside in a vehicle width direction of the hybrid vehicle and a portion covering the second region from outside in the vehicle width direction, the portion covering the second region being located inwardly of the portion covering the first region in the vehicle width direction.