A plurality of paint spray guns are directed substantially perpendicularly toward respective vertically divided surfaces of a side panel of a workpiece such as an automotive body. The paint spray guns are spaced in a direction in which the workpiece is delivered and being disposed at different heights, respectively. Paint sprays are ejected from the paint spray guns toward the workpiece which is being delivered in the direction. Simultaneously, the paint spray guns are displaced back and forth perpendicularly to the direction and substantially parallel to the surfaces of the side panel to coat the surfaces respectively with the paint spray guns, thereby coating the side panel.
