To make two tractive bodies so as to be simply and positively lockable for their connection when these tractive bodies of a longitudinal trailer main body are vertically superposed on each other.

One end side tractive body 5 and the other side tractive body 6 towing a trailer main body 2 both are rotatably installed in a cross direction intermediate section at both these one end and the other end sides of this trailer main body 2. When the longitudinal trailer main body 2 is connected to both these one end and other end tractive bodies 5 and 6 by these tractive bodies 5 and 6, an each connecting means 101 connecting these tractive bodies 5 and 6 vertically superposed on each other is installed there respectively. In this connecting means 101, a fitting projection 85 is saliently installed on each base end side of these tractive bodies 5 and 6, and each fitting hole 84 rotatively fitting two fitting projections 85 of the longitudinal trailer main body 2 is formed on each tip side of these tractive bodies 5 and 6. In addition, each connecting body 112 connecting the vertical tractive bodies 5 and 6 in a state that the fitting projections 85 are fitted in the fitting holes 84 and these tractive bodies 5 and 6 are superposed on each other is installed in both the one end and the other end tractive bodies 5 and 6, respectively.