In a transmission control device, a controller determines failure of a rotation sensor. A hydraulic control circuit and the controller variably control a speed ratio of a variator. The hydraulic control circuit and the controller variably control a gear position of a sub-transmission mechanism, and in a case where the failure is determined, fix the gear position of the sub-transmission mechanism to first speed. The hydraulic control circuit and the controller fix the gear position of the sub-transmission mechanism to the first speed during a vehicle stop in a case where the gear position of the sub-transmission mechanism upon a determination of the failure is second speed.