To simply and quickly switch fixed location stopping operation to/from outside stopping operation.

A 1st stopper 3 out of 1st and 2nd stoppers 3, 4 fitted to one member 2 to be relatively moved together with the other member 1 is displaced while being displaced retractably between a normal location capable of abutting on a detection means 5 and stand-by location not abutting thereon by a displacement driving means 22, and respective stoppers 3, 4 are detected by a detection means 5 fitted to the other member 1. Then the 1st stopper 3 is rotatably pivoted, and when a state that the 1st stopper 3 exists between the detection means 5 and the 2nd stopper 4 is changed to a state that the 1st stopper abuts on the detection means 5, the rotation of the 1st stopper 3 is suppressed to maintain the abutting posture of the stopper 3. When the 1st stopper 3 and the detection means 5 abut on each other along the reverse direction, the rotation of the stopper 3 is allowed to release the abutting posture.