PURPOSE: To prevent the mixing of a coating material in the next coating material effectively, by cleaning the previous coating material remaining in the pipeline with a high-speed purging air in color change, and by injecting a colorless transparent cleaning clear coating material into the pipeline.

CONSTITUTION: The operation of the previous coating material feeder 21 is stopped, and the solenoid valve 58 is opened and closed intermittently to inject the high-pressure purging air A1 from the feed pipe 9 into the previous coating material feed pipe 7 and the main coating feed pipe 2. The solenoid valve 52 is opened to close the pinch valve 8, and the solenoid valve 50 is closed to open the pinch valve 4. The solenoid valves 71 and 59 are opened to inject the main purging air into the pipeline 2 and the purging air A2 into the pipeline 7 and 2, and the solenoid valve 44 is controlled to feed the high-speed carrier air set at a high pressure by the regulator 40 into the cleaning coating material fluid tank 45. The colorless transparent cleaning clear coating material is injected from the feeder 16 into the pipeline 2 to purge or to cover and enclose the previous coating material remaining in the pipeline 2.