An electric power steering apparatus comprises a motor for applying an auxiliary torque to a steering system, a steering torque sensor for detecting a steering torque in the steering system and a control unit for drive-controlling the motor based on at least a steering torque signal from the steering torque sensor. The control unit includes a motor control unit and a failure detecting unit for detecting a failure of the control unit. Based on a failure detection signal from the failure detecting unit, the motor drive control unit switches over from a normal mode in which no failure exists in the apparatus to a first failure mode in which a certain failure exists in the apparatus and an assist ratio is changed to about half of that of the normal mode.
