A paint cartridge (31) is provided with a wash fluid passage (43) which is in communication with a paint chamber (36), along with a wash fluid valve (45) which is adapted to open and close the wash fluid passage (43). Provided on the side of a replenishing stool (52) are a replenishing valve (61) which supplies or discharges paint to or from the paint chamber (36), an extruding thinner feed/discharge valve (86) which supplies or discharges paint-extruding thinner to or from an extruding thinner chamber (37), and a wash fluid supply valve (101) which supplies a wash fluid to the paint chamber (36) through the wash fluid passage (43). Accordingly, upon opening the replenishing valve (61), wash fluid supply valve (101) and wash fluid valve (45), a wash fluid from the wash fluid supply valve (101) is allowed to flow into the paint chamber (36) through the wash fluid passage (43) and discharged through a feed tube (34) to wash away deposited paint therefrom.