PURPOSE: To increase a pressing force so as to grip a heavy tool sufficiently certainly by supplying a pressure liquid to a piston when a finger part is locked at a closed position, and discharging the pressure liquid when the lock is released, according to switching of a switching valve.

CONSTITUTION: When a tool gripping arm 1 is moved to grip a tool 17, a pressure liquid is discharged from a piston 21 so that force is not acting or force of a weak spring 48 only is acting on a movable finger 16, and therefore the finger part 12 can grip the tool 17 without turning of the tool 17. After the gripping, the pressure liquid is supplied to the piston 21 to bring the movable finger 16 into a locked state for gripping the tool 17 securely to draw it out of a machine tool or a tool storage part. When the tool 17 is inserted into the machine tool or the tool storage part, the pressure liquid is being supplied until the tool insertion is completed, so as the lock the movable finger 16 in a closed state. When the insertion is completed, the pressure liquid is discharged to move a tool gripping arm 1 with the movable finger 16 being in the state of smooth moving, thus eliminating the insertion of the tool 17 in a tilted state into a main spindle and the like of a machine tool.