The wrist assembly of an industrial robot comprises a first wrist portion (21) provided on the free end of the robot arm (20) and having a pair of projections (22, 23) in parallel with each other on the fore-end thereof. A second wrist portion (24) is provided between the projections of the first wrist portion and supported on both of the projections so as to be rotatable about a first axis (.beta.) intersecting a longitudinal axis of the robot arm at a right angle. A third wrist portion (25) is supported on the second wrist portion so as to be rotatable about a second axis (.alpha.) intersecting the first axis at a right angle, and constructed to allow work attachments to be attached to the front end thereof. A first motor (45) and a second motor (55) are used for driving the second wrist portion and the third wrist portion. A first power transmission mechanism (I) for transmitting a driving force of the first motor to the second wrist portion includes a pair of first hypoid gears (35, 36) provided in one of the projection of the first wrist portion and meshed with each other. A second transmission mechanism (II) for transmitting a driving force of the second motor to the third wrist portion includes a pair of second hypoid gears (51, 52) provided in the other projection of the first wrist portion and meshed with each other.