To heighten the stability in running of a plurality of trailers coupled together free of the risk that wheels turn left and right even if they run on an uneven surface part, etc., of a road.

Wheels 3 on the left and right at one end of a trailer body 2 and ones 3 on the left and right at the other end are supported rotatably by a wheel supporting mechanism 4. A one-end tractive body 5 and an other-end tractive body 6 are rotatably installed in the one-end middle part of the trailer body 2 and in the other-end middle part. A steering mechanism 7 steers wheels 3 by turning the tractive bodies 5 and 6. A plurality of such trailer bodies 2 are coupled together by these tractive bodies 5 and 6 opposing to each other. The wheel supporting mechanism 4 is equipped with a shaft holder 21 fixed to the trailer body 2, an axle body 24 having a center shaft 22 for wheel rotation inserted rotatably in the shaft holder 21 and an axle 23 on which the wheels 3 are supported rotatably, and a braking means 25 to brake the axle body 24 and keep the trailer body 2 in straight running.