present invention provides the step of pre ohp instead of setting the maximum electric current time longer than the related art such that all the maximum electric current of 65 a is not substantially supplied but electric current that is gradually decreased from the maximum electric current is supplied even during the maximum electric current time and the heating load that is applied to the motor can be maintained substantially at the same level by relatively more rapidly decreasing the electric current supplied to the motor than the related art in the step of ohp after the maximum electric current time the above method substantially extends the time taken to reach the step of ohp and as a result this means that relatively larger amount of steering can be performed until the ohp operation thereby improving the ohp performance further when the electric current supplied to the motor is decreased to more rapid second electric current reduction coefficient than the related art in the step of ohp the steering force supplied from the motor is rapidly decreased and the driver feels the steering wheel heavy however the driver cannot substantially recognize a change in the feeling as compared with the related art that the electric current is.