(57) An automatic spray gun has liquid atomizing means (1) provided at the front end thereof, a needle valve (3) adapted to control the amount of a liquid jetted out from the atomizing means (1), and an air piston (4) received in a cylinder (5) at the rear end of the needle valve (5) and activated by means of compressed air. The spray gun is provided with distance measuring means (17) for judging the distance between the spray gun and an object to be sprayed which is positioned in front of the spray gun, and a solenoid valve (11) activated in response to an ON-OFF signal delivered from the distance measuring means (17), the solenoid valve (11) being disposed in an air passage (12) which extends from a compressed air supply source to the cylinder (5). Thus, the needle valve (3) is selectively opened and closed by controlling the solenoid valve (11) so as to start and stop a spraying operation automatically.