PURPOSE: To reduce frequency of overload generation by constituting a joint between a contact body and a wagon so that the contact body may be displaced in vertical and horizontal directions at a wagon bottom part and the force which the contact body receives may extend diagonally to the upper toward the wagon.

CONSTITUTION: A contact body and an endless belt 2 are moved so that they may be disengaged from each other with racks 6, 7 engaged. At a joint mechanism 5 installed between the bottom base frame 8 of a wagon 1 and the contact body, there are provided upper and lower plates 10, 13 which come into contact with the wagon 1 and the contact body 1. Moreover, upper link rods 11a, 11b and lower link rods 14a, 14b are connected by middle pins 15a, 15b of middle link 16. As a result, the force which the contact body receives at the time of driving a belt 2 is transmitted to the wagon 1 upwards, and the wagon 1 is moved by its horizontal component force, so that moving impact load is decreased, and the action which is pressed against the belt 2 is given to the contact body 4, thus preventing the racks from being disengaged.