A cartridge discharges paint in a paint chamber from a feed tube by displacing a piston in a tank. A waste liquid adjusting valve located on a downstream side of a waste liquid passage on-off valve and including a throttle passage is provided in a waste liquid passage to be connected to the feed tube. This waste liquid adjusting valve is opened at the time of washing clean the paint chamber and a paint supply passage of the feed tube to widely enlarge the passage cross-sectional area of the waste liquid passage. When paint is replenished into the paint supply passage, the waste liquid adjusting valve uses the throttle passage as a flow passage to narrowly throttle the passage cross-sectional area of the waste liquid passage. The amount of discarded paint which flows out from the feed tube is thereby reduced.