An apparatus for testing power transmission belts is disclosed, wherein at least one test belt is mounted between at least one drive and driven motors each having corresponding numbers of drive and driven pulleys, respectively. The pitch diameter of the drive pulley is larger than that of the driven pulley to generate electric power in the driven motor. The test belt is subject to various loads due to torque variation of both drive and driven motors or either one of the motors by connecting a transformer to both or either one of the motors.