Abstract: An automatic painting system including a non-explosion-proof automatic painting machine which has an arm having a spray gun and an arm housing, the arm and the arm housing being inserted through an opening defined in a side wall of a closed painting booth into the interior of the painting booth. A hermetically sealing bellows is mounted on and extends between a distal end of the arm and an inner surface of the side wall around the opening therein for protecting a portion of the arm which is slidable with respect to the arm housing from the atmosphere in the painting booth. The interior of the bellows is kept in communication with the atmosphere through the opening in the side wall.