In a transmission device, a power roller transmits a rotational driving force from an input disc to an output disc in a transmission ratio (transmission gear ratio) corresponding to a tilt motion angle. The power roller allows the transmission ratio to be changed in such a manner that the position of the trunnion on which the power roller is tiltably supported is changed by a trunnion drive mechanism. Hydraulic oil is supplied from a hydraulic pump to the trunnion drive mechanism via a direction selector valve. The direction selector valve selects a flow direction of the hydraulic oil to supply the hydraulic oil to a speed reduction chamber or a speed increase chamber of the trunnion drive mechanism, and discharge the hydraulic oil from the other. In a case where a discharge condition is met, the controller controls a movement of the discharge valve to discharge the hydraulic oil from the speed increase chamber.