To improve coupling workability, and to reduce back lash of a connection part of vehicles.

One of two vehicles is provided with a connecting shaft 3 vertically movable, and the other has a connection hole 5 into which the connecting shaft 3 is removably inserted. The connecting shaft 3 is movable downward in a shaft length direction by its own weight or by urging force. Also, the one of the two vehicles is provided with a regulating body 4 pivotally supported so as to be swingable in a lateral direction, and engaged with a lower end of the connecting shaft 3 to regulate movement downward of the connecting shaft 3. The connecting shaft 3 is inserted into the connection hole 5 by the swing of the regulating body 4 without operating the connecting shaft 3.