Wrist mechanism of industrial robot

A wrist mechanism of an industrial robot is described which comprise first, second and third wrist elements rotatably supported relative to each other around respective rotation axes which are mutually inclined, which leaves a hollow space inside thereof free for passage of supply cables and pipes which are to be connected to a tool being secured to the robot wrist. The second and third wrist elements carries first and second ring-shaped hollow reduction units, and their respective output shafts rotates the second and third wrist elements, respectively, thereby the amounts of backlashes and flank wears in the transmitting gears as well as the amounts of reflected rotational movements of the second and third wrist elements affected by the rotational movements of the first and second wrist elements are reduced within fractions of the reduction ratios of each of the reduction units, which result the controllings of the positionings of the wrist elements become easy and accuracies thereof are increased.