A vehicle power assist system can be applied to a vehicle with a driven wheel (4) that is mechanically unconnected to a main drive source (5) such as an internal combustion engine. The driven wheel (4) is supported by a wheel support bearing assembly (31) to which a drive assist, motor generator (8) is mounted. A rotor of the motor generator (8) is directly fixed to a rotational ring of the wheel support bearing assembly (31) without interposition of a speed reducing mechanism or a speed increasing mechanism. The vehicle power assist system includes a power storage unit (19) configured to store a regenerative power generated by the motor generator (8) and to supply the stored power to the motor generator (8).