A small autonomous vehicle is required in greenhouse production and a small open vegetable field for automatic spraying, carrying, harvesting etc. This study uses simple structural guidance of horticultural cultivating materials to develop an automatic guided vehicle. The developed vehicle has four wheels: two front steering wheels, and two rear driven wheels. The vehicle has a detection unit, a steering unit, and a control unit. The detection unit has two extension rollers and a potentiometer; its function is to detect the distance from the vehicle to the guided material. The control method is used for adjusting the ON/OFF control of the front wheel steer by detecting the distance between the objective material and the vehicle. The driving tests were conducted on a plastic film covered soil surface of a greenhouse isle, the concrete surface of a greenhouse central road, and in the open field. The results of the straight driving control displayed absolute maximum errors of 35 mm, 23 mm, and 29 mm on the covered soil path, concrete path, and in the open field, respectively. The test results proved that the straight driving control of the developed system was sufficiently accurate to be used for spraying and carrying operations.