In an industrial robot having a plurality of arms, each arm is coupled with other elements, such as a mounting base, another arm, a robotic hand, and revolved by a motion of the revolvable joint. The revolvable joint has a rotary electric connecting structure such as a slip ring or a rotary transformer which can be rotated endlessly. Electric powers for driving motors by which the arms are revolved and control signals for controlling the driving of the motors are supplied or transmitted through the rotary electric connecting structure, so that the arms can be rotated endlessly without twisting or breaking of electric cables.