Control apparatus

A control apparatus controls a motor of an electric power steering system including: an input shaft connected to a steering member; a column shaft connected to the input shaft; a turning device that includes a rack and pinion mechanism, and turns a wheel; and the motor. The control apparatus includes a reliability computation portion that computes a reliability according to an abnormality detection state regarding at least one of a current sensor, a torque sensor, and a rotational angle sensor; a steering-shaft load estimation portion that estimates a steering shaft load using a current corresponding value, a torque corresponding value, and a rotational angle corresponding value; and a weight changing portion that changes a weighting of the current corresponding value, the torque corresponding value, or the rotational angle corresponding value according to the reliability.