PURPOSE: To simplify the constitution by allowing a single fluid pressure cylinder to perform two actions, i.e. gripping and release of a tool socket and its transport between two positions.

CONSTITUTION: A swing arm 47 is installed on a base, and reciprocates with a rotational center 45 as fulcrum, and a fluid pressure cylinder 49 drives the swing arm 47 into reciprocation. A socket gripper 51 is fitted at the tip of said swing arm 47, and reciprocates along a guide rail 53 fixed at the oversurface of the base when the tool socket is transported. When an expansion rod 55 of said fluid pressure cylinder 49 is elongated, the swing arm 47 moves with socket gripper 51 to the tool exchange position 39, and when contracted, the arm moves with the same to the tool socket handover position.