PURPOSE: To make the thickness of a coating film uniform, while making a coating process automated, by sucking paint mist sprayed through a nozzle inserted into one opening of a tubular member by a evacuative suction means attached to the other opening.

CONSTITUTION: In coating the inner surface of a sill as a part of an automobile body, when said body comes in a state stationarily supported with a lifter, a nozzle 7 is automatically inserted through an air cylinder into the vicinity of the opening of the sill 3 at its one opened end 3a, and a suction cup 10 is closely attached to the other opened end 3b. Thereafter, air and paint are individually supplied to a spray gun 8 and atomized in a mixed state through the nozzle 7, so that paint mist having permeated the interior of the sill 3 is sucked at the side of the suction cup 10 communicating to a cyclone 12. At this time, paint particles adhere onto the entire inner surface of the sill 3. Said sucked paint mist is separated from air and recovered.