A runner 5 including a striker 51 in a lower portion; a catcher 6 corresponding to the striker 51 and engaging a movable body 1 in a reference position R; and an urging device 7 storing an urging force when the catcher 6 is in the reference position R, are provided. The catcher 6 in the reference position R captures the striker 51 of the runner 5 stopped and engaged with a rail 2 in a self-propelling start position SA of the movable body 1, and upon this capture, an engagement between the catcher 6 and the movable body 1 is released. At the same time, due to a backward movement of the movable body 1 from the stop position SA, the catcher 6 is positioned in the reference position R again, and releases the striker 51 of the runner 5. An engagement between the runner 5 and the rail 2 is subsequently released.