A transmission testing apparatus employs an electric motor as a driving power source. The electric motor is coupled with a speed increasing device for providing engine speed equivalent revolution speed at low speed for realizing engine equivalent low inertia characteristics. The electric motor is associated with a control unit which stores engine torque simulated torque variation characteristics, one of which is selected on the basis of an engine load simulated value. The control unit controls the output torque of the motor toward a torque demand derived on the basis of an engine speed simulated value derived according to the selected one of torque variation characteristics.