To provide a controller apparatus of a type, in which the controller is given the redundancy so that the control of the drive motor can be properly performed at all times when an abnormality such as the failure of the controller occurs, with the reliability consequently increased, a plurality of controllers are provided, each including a power circuit for outputting a drive current for the drive motor and a control circuit, which is a light electric circuit, for controlling the power circuit in response to a motor drive command fed from a higher control. An abnormality determiner is provided for determining an abnormality occurring in the controller then in use according to a prescribed rule and then generating a switching signal. A switch is provided, which is operable in response to the switching signal to change the controller then in a state of functioning relative to the drive motor.