PURPOSE: To insert a pin into a hole without applying a large force to the pin and a tool shaft, etc., in a condition of increasing the compliance of an arm by cutting off the driving source of the arm after moving the tool shaft onto an operation point by the action of the arm and lowering the tool shaft in this condition.

CONSTITUTION: When the center of a pin 3 is shifted with respect to the inserting hole 2 as shown by the solid lines at the time of lowering a tool shaft 17, the pin 3 is brought into contact with the chamfered tapered opening end of the inserting hole 2 and slides down along the taper face 2a of this opening end. At this time, since both I-shaft and II-shaft servomotors which are the driving sources of arms 15, 16 are not electrified leaving both arms 15, 16 in a freely revolvable condition, the pin 3 slides down on the tapered face 2a while revolving the arms 15, 16 a little in the arrow A, B directions from the solid line positions. As the end portion of the pin 3 is fitted into an inserting hole 2, the pin 3 becomes coaxial with the inserting hole 2 and the rotation of the arms 15, 16 is also stopped at this point of time.