A clutch motor (30) having an outer rotor (32) and an inner rotor (34) that are both rotatable and being relatively power run or regeneratively driven is provided on an output shaft of an engine (50), and the output of the clutch motor (30) is transmitted to front wheels (26, 28) via a driving shaft (22A). On the other hand, an assist motor (40) is directly coupled to a driving shaft (22B) for transmitting power to rear wheels (27, 29). The clutch motor (30) can regenerate a part of the energy of the engine (50) through sliding rotation. Torque can be outputted to the two shafts by driving the assist motor (40) by at least a part of regenerated energy or energy stored in a battery (94), thus effecting a so-called four-wheel driving. In addition, the clutch motor (30) can be overdriven while performing regeneration by the assist motor (40). In a construction using a planetary gear (120) and motors (MG1, MG2) which replaces the construction in which the clutch motor is used to distribute the power of the engine, the power is distributed by the planetary gear (120), and the power is transmitted to one of the shafts through the output of the planetary gear (120) and to the other shaft via the motor (MG2), thus four-wheel driving being effected.