An object of the present invention is to detect the generation of a drag torque in a locking mechanism, in a hybrid vehicle in which a speed change mode can be changed between a fixed speed change mode and a stepless speed change mode by the action of the locking mechanism. In a hybrid vehicle, a brake mechanism is a wet multiplate brake apparatus and can selectively lock a motor generator. On the other hand, in a case where the drag torque is generated in the brake mechanism, if the motor generator is in a positive rotation state, an actual motor generator torque (first torque) is greater than a torque (less as a reaction torque, second torque) calculated from the operating condition of the hybrid vehicle by the amount of the drag torque. If the motor generator is in a negative rotation state, the first torque is less (greater as the reaction torque) than the second torque. The ECU uses this phenomenon to detect the drag torque.