A motor vehicle steering system includes a motor driving circuit connected between a power supply and a ground for driving a multi-phase motor, PWM signal generating unit for generating an each-phase PWM signal for controlling a current flowing through each of phases of the multi-phase motor and feeding the each-phase PWM signal to the motor driving circuit, a single current sensor connected between the motor driving circuit and the power supply or the ground, and each-phase current value computing unit for finding an each-phase current value flowing through each of the phases of the multi-phase motor on the basis of an output of the current sensor. The PWM signal generating unit shifts the fall or rise timing of a carrier wave of the each-phase PWM signal by a predetermined phase shift amount.