PURPOSE: To secure and enhance stable steering feeling by estimating disturbing torque with the revolution and current of an assist motor detected, and thereby compensating the assist command in such a way as to cancel the aforesaid disturbing torque.

CONSTITUTION: The current of an assist motor 10 is detected by the armature current detecting section 66 of a current control section 60 so as to be inputted into the disturbing torque estimating section 52 of a disturbing torque compensating section 50. The disturbing torque estimating section 52 inputs the revolution of the assist motor 10 which is detected by a steering angular velocity detecting section 51, so that disturbing torque is estimated based on the current and revolution of the motor. The estimated value is added to the assist command outputted from an assist command section 20 so as to be compensated. The compensated assist command is added to and/or subtracted from the outputs from a viscosity compensating section 30 and an inertia compensating section 40 so as to be outputted to the current control section 60. The assist motor 10 is controlled in such a way that the disturbing torque is compensated. By this constitution, stable steering feeling can thereby be secured and enhanced.