Abstract: A joint device according to the present invention is attached to each of a plurality of arm units which constitute an arm of an industrial robot, and is used to connect a first arm unit and a second arm unit adjacent thereto, and to rock the arm units. The joint device comprises a coupling mechanism which connects the first and second arm units for rotation around specified axes. A first gear train, which includes a plurality of gears, is provided in the first arm unit, and has a rotatory-force transmission path through which the gears thereof successively transmit a rotatory force. A first rotatory-force source is used to transmit the rotatory force to the first gear train. The second arm unit is constructed in the same manner as the first arm unit. A clutch mechanism serves to permit and interrupt the transmission of the rotatory force through the rotatory-force transmission path of the first gear train.