The invention provides a motor-driven
wheel drive device in which the durability of a wheel bearing is increased, the weight and size thereof are reduced, and the disassembly and reassembly thereof is taken into account. [MEANS FOR SOLVING PROBLEMS] This motor-driven
wheel drive device comprises a drive part (4) having an
electric motor (M) driving a planetary
speed reduction gear (2) installed in the wheel bearing (1) and a rotating member (17). The wheel bearing (1) further comprises a hub wheel (6) on which an inside rolling surface (6a) is formed, an inner ring (7) press-fitted to the hub wheel, an outer member (8) in which double rows of outside rolling surfaces (8a) are formed, and rolling elements (9). The planetary
speed reduction gear (2) further comprises a sun gear (3) formed in a rotating member (17), a plurality of planetary gears (12) disposed between the outer member (8) and the sun gear (3), and carrier pins (14) pivotally supporting these planetary gears on a connection shaft (13). The drive part (4) further comprises the
electric motor (M) releasably disposed on the outer member (8) and the rotating member (17). The connection shaft (13) is connected to the hub wheel (6) through a
serration, and the rotation of the
electric motor (M) is transmitted to the hub wheel (6) through the rotating member (17) and the planetary
speed reduction gear (2).