A microcomputer-controlled unmanned air blast sprayer was developed to avoid the operator’s exposure to agricultural chemicals or mechanical noise, and to improve the work efficiency during application for pest control in orchards. The developed sprayer moves automatically without a driver along a guiding cable, which is set up along the work course between the tree rows of the orchard. Unmanned application system developed controls automatically steering gears of the sprayer by detecting a magnetic field, which was generated by feeding an alternating current to the guiding cable. The cable can be installed underground (at a depth of less than 30 cm), on the ground surface, or at a height of 150 to 200 cm from the ground along the work course. The maximum total length of the cable is about 1,000 m. During unmanned application, the machine sprays agricultural chemicals automatically along the work course. However, if it is unnecessary to spray outward at the end of the tree rows where the sprayer turns, the machine is able to stop spraying outward while turning, due to a special system. All the functions of the sprayer stopped automatically when the sprayer reached the end point of application work. The sprayer has several safety devices controlled by the unmanned application system to avoid any accidents during unmanned application work. As a result of the performance test, deposition of sprayed chemicals on the fruit trees and work efficiency by this sprayer were as good as in any conventional manned air blast sprayers.