When a failed Hall IC cannot be identified through determination as to whether any of output voltages falls outside a predetermined output range and determination as to whether any of the output voltages has steeply varied, a microcomputer determines whether the directions of steering torques converted from the output voltages are the same. Then, when the directions of the converted steering torques are the same, the average of these output voltages is used to calculate a temporary torque, and then power assist control is continued, that is, specifically, assisting force applied to a steering system is slowly and gradually decreased, on the basis of the temporary torque.