A steering angle .theta.t detected by the torque sensor is read at S900. Then, an electrical angle .theta.m corresponding to a motor rotational angle is read at S902. At S908 through S922, motor rotational numbers are calculated based on .theta.t, .theta.m and the rotational number of a handle, and a correct rotational number of the handle is calculated from the motor rotational number which is the nearest to an integer of all of the calculated motor rotational numbers. Thereafter, an absolute steering angle which is not influenced by various errors is calculated based on the calculated rotational number of the handle and the steering angle .theta.t detected by the torque sensor.