A motor-driven power steering system includes a steering column connected to a steering wheel, a motor with a rotation shaft connected to the steering column, a decelerator that rotates by interacting with the rotation shaft, fixing parts mounted at each left and right wheel, link members rotatably connected at both ends to the fixing parts and the decelerator, a detecting part that detects the vehicle state, and a motor driving device that generates a steering assist force by supplying the motor with a current determined on the basis of the vehicle state. This configuration transmits the driving force of the motor directly to vehicle wheels, thereby optimizing the motor function and reducing the vehicle weight by eliminating a rack.