A panel (9) is conveyed by using a conveyer (3), and the coating surface of the panel (9) is divided into two coating areas (CAa, CAb). Further, the coating areas (CAa, CAb) are coated by reciprocating sprayer units (6, 7) parallel to a conveying direction. At this time, at a boundary between the coating areas (CAa, CAb), the positions of turning paths (Ta0, Tb0) of the reciprocation of a coating machine are shifted sequentially from the front side to the rear side in the conveying direction, so that coating trajectories (Ta, Tb) like a series of steps are formed. Thus, at the boundary between the coating areas (CAa, CAb), the turning paths (Ta0, Tb0) can be spread and located, and the occurrence of color shading can be prevented.