A device for controlling a steering transmission ratio variable device, which is provided with: a motor, which is able to apply a driving force that promotes relative rotation between a steering output shaft coupled to wheels to be turned and a steering input shaft that applies a steering input to the steering output shaft to one of either the steering output shaft or the steering input shaft a motor driving device that drives the motor and a locking device that is able to restrict the relative rotation, has a setting device that prescribes a drive voltage the motor and sets a damping gain, which acts in a direction that reduces a rotating speed of the motor, to a value that is larger than a reference value corresponding to an unlocked state during a locking control period in which a state of the steering transmission ratio variable device switches from an unlocked state in which the relative rotation is not restricted to a locked state in which the relative rotation is restricted.
