PURPOSE: To efficiently perform washing by incorporating a washing process in a line, by making a washing tank having a plurality of nozzles arranged thereto displaceable to a washing work position where a painting gun can be introduced into the tank from a retracted position.

CONSTITUTION: An upper painting gun washing mechanism 136 for washing the painting guns 90aW90d of an upper painting mechanism is formed in a freely revolving, rising and falling manner and preliminarily retracted from the feed path of a car body 14 at the time of painting and displaces respective washing tanks 148aW148d to a predetermined position, where the painting guns 90aW90d must be washed, at the time of washing work. At this time, the painting guns 90aW90d are displaced in the direction shown by an arrow A to be simultaneously introduced into the hole parts provided to the flexible cover members of the washing tanks 148aW148d and the nozzle parts of the painting guns are washed with the solvent injected from a washing gun. Further, even in said painting gun washing mechanisms 138, 140, side part painting guns are washed simultaneously and efficiently in the same way.