A force motivating a strut to incline itself in the running direction (front-and-rear direction) of a movable main body is produced by impact stress caused by accelerating, decelerating or stopping the operation of a delivery device. Such force can securely be received by a bottom frame structure as well as by a reinforcing structure of the portions of projected corner members protruding in the running direction which are formed integrally with a cylindrical body of the strut at respective corners thereof. A force motivating the strut to incline itself in the direction orthogonal to the running direction is produced by inward/outward load delivery operation by means of a delivery instrument provided on a carriage. Such force can also securely be received by the bottom frame structure as well as by the reinforcing structure of the portions of the projected corner members protruding in the orthogonal direction.