To attain good steering characteristics by generating steering assist effort so that steering holding power may be minimum in an optimum steering angle necessary for traveling with a detected road curvature and at a vehicle speed detected by a vehicle speed detecting means.

A controller 15 calculates an optimum steering angle passing through a corner based on an inputted road curvature ρ and a vehicle speed detected value V, calculates steering assist torque for minimizing steering holding power to travel at a corner with a vehicle speed detected value V based on the steering angle and the vehicle speed detected value V, and outputs pulse current corresponding to the steering assist motor 13. Where the steering assist torque command value of the controller 15 and the actual steering assist torque are equal to each other and there occurs no delay, it acts as power steering in the case of running without steering effort control, and the steering assist torque is determined based on the steering torque of the steering torque sensor 17 and the vehicle speed detected value V of the vehicle speed sensor 18. The current corresponding to it is outputted to a steering assist motor 13 to generate steering assist torque.