A device for driving a vehicle including an engine that serves as a power source of the vehicle, and a transmission that is connected to the engine, the engine and the transmission being arranged transversely such that an axial direction of an output shaft of the engine accords with a right-left direction of the vehicle includes a motor generator (MG) that serves as a power source of the vehicle, and a speed reducer that is connected to the MG. The MG and at least a part of the speed reducer are arranged outside of an engine compartment that accommodates the engine and the transmission. An output shaft of the speed reducer is connected to a power transmission system, which transmits power of an output shaft of the transmission to a drive shaft of a vehicle wheel to be capable of transmitting its power to the power transmission system.