PURPOSE: To simplify the operating position of fixing pins by setting the axial center of fixing pins installed at both sides in the rear chassis so that it may align with the rear dump center of a cargo case.

CONSTITUTION: The aixal centers of fixing pins 10 and 10' are set to align with the rear dump center of a cargo case 8 so that those pins may be removed from the driver's seat. Under this construction, the cargo case 8 is lowered to the chassis 1 and then rear fixing pins 10 and 10' are set to a locking position. Front fixing pins 9 and 9' are then reliesed and rear engaging pieces 5 and 5' are fastened to supporting pins 7 and 7'. The cargo case 8 is slanted in the rear direction by extending a dump cylinder 12 not illustrated in the figure. As the fixing pins 10 and 10' align the cargo case 8 with the rear dump center, the engaging pieces 5 and 5' turns around the center of the fixing pins 10 and 10'. When the cargo case is transversely slanted, the fixing pins 9 and 10 or 9' and 10' are paired. One pair is locked while the other pair is reliesed. With this construction, the operating position can be simplified.