PURPOSE: To prevent uneven painting due to stop of conveyor, by increasing the paint device painting the side sill by the speed corresponding to the mobile speed of conveyor at conveyor stop and by moving it at a given speed normally, to the car body on the conveyor.

CONSTITUTION: When the car body 1 on the truck 4 of the conveyor 3 moves to the paint position in a given speed, the 1st detection means of the limit switch 22 and photo electronic tube 23, detects it, and the paint unit 5 pushes the frame 11 providing the spray gun 10 toward the car body via the cylinder 9 while is it stopped. The frame is shaken right and paints the front end 2a in flange shape of the side sill 2. Next, the motor 7 is driven, the paint unit is moved to reverse direction of car body in a given speed to paint the side 2c of the side sill 2. When the paint unit reaches the rear end 2b of the side sill, it is stopped to paint the rear end 2b. If the conveyor 3 stops during paint, the 2nd detection means detects it, and the motor 7 increases the mobile speed of conveyor to a given speed.