In an electric power steering system, an ECU 11 includes two independent microcomputers 17a, 17b that serve as motor control signal generators, and the microcomputers 17a, 17b perform the same current feedback computation. Switching arms 20a, 20b that constitute a driving circuit 18 operate independently of each other, based on motor control signals generated by the corresponding microcomputers 17a, 17b. Each of the microcomputers 17a, 17b determines whether an absolute value of a current deviation of an actual current I (I1, I2) from a current command value exceeds a predetermined threshold value. If the current deviation exceeds the threshold value, it is determined that an abnormality occurs in the system.