An index table assembly includes a rotary table, a frame separated from the rotary table in the direction of a rotational axis of the rotary table, a clamping device for bringing the rotary table into contact with the frame by moving the rotary table along the rotational axis, a first bearing disposed between the rotary table and the frame, and an urging device disposed between the first bearing and one of the rotary table and the frame and pressing the first bearing against the other one of the rotary table and the frame at least when the rotary table rotates.