To provide a tractor that can prevent contact between vehicles by warning the driver of the tractor when there is a risk of contact between the tractor and a trailer or between trailers at a course change or turn during traction travel, and an oversteer warning system that raises such a warning.

The tractor 1, which has a travel system 4 for running a vehicle body 2, a steering system 5 for changing the course of the vehicle body 2 and a traction device 3 for coupling a trailer, comprises the oversteer warning system 10 for warning the driver when there is a risk of contact between vehicles at steering. The driver, when warned, refrains from oversteering to prevent contact between vehicles. The oversteer warning system comprises steering detecting means or coupler detecting means, and warning means.