In order to promote sericultural labor-saving and to decrease costs, this study was carried out to develop an automatic steering system for a compact tractor used in mulberry fields. A new experimental vehicle for automatic steering was developed characterized by hydraulic transmission, front-wheel drive, and microcomputer control. A magnetic azimuth sensor and an ultrasonic sensor were selected as noncontact-type position sensors. Then, the sensor systems were developed to determine the positions automatically by using a microcomputer. Moreover, an automatic steering system that consisted of a microcomputer (8-bit CPU), the position sensor systems and the vehicle was developed and tested. As a result, the system enabled to control the travel of the vehicle in a mulberry field.