To facilitate reverse of combination vehicles by steering wheels of a trailer so that a turning center of a tractor and a turning center of the trailer coincide with each other when the comvination vehicles are moved in reverse.

When a mode changeover switch 40 is set to an automatic mode, a target connecting angle, at which a turning center of a tractor 1 and a turning center of a trailer 2 coincide with each other, is computed on the basis of the detection information from a tractor steering angle sensor 14 when connected vehicles 3 are moved backward, and a trailer steering device 19 is controlled so that a connecting angle detected from a connecting angle detection sensor 17 coincides with the target connecting angle. When the mode changeover switch 40 is set to a manual mode, steering angles of trailer wheels 20a, 20b are set by a driver. In this way, reverse movement of the connected vehicles 3 can be result carried out.