A stereo vision system for agricultural tractors was developed. Two kinds of stereo camera unit were manufactured: one of which is mounted on the front of the tractor and the other on the cabin roof. The system can detect various formed or shaped objects, such as crop rows, ridges, uneven surfaces after tilling and marker traces in front of the tractor in agricultural fields. The system generates distant images with a 0.1-second cycle, while an internal algorithm installed in the system analyzes this distant image data three-dimensionally, and detects the positions of objects. The positional data was transferred to a steering controller of the tractor and tilling work was performed automatically by tracking these objects.