A power steering system for a vehicle includes a steering shaft with its rear end in connection with a steering handle and with its axis inclined forwardly downwards. An electric motor is disposed with its axis orthogonal to a plane containing the axis of the steering shaft. The electric motor applies a steering force to the side of a steering wheel or wheels according to an operational torque exerted on the steering handle. This enables the power steering system to be easily applied to a vehicle in which the portion on the front side relative to the steering handle is short. A steering shaft is rotatably supported on a support case, at least a part of which is disposed on the inner side of the rotational locus of a steering handle in plan view. The rear end of an electric motor mounted to the support case is disposed on the front side relative to the rear end of the steering shaft.