A paint supply method supplies a paint into a paint cartridge by using a filling valve that has: a paint supply channel that is linkable in communication with a supply portion provided for supplying the paint into the paint cartridge; a branch channel that branches from the paint supply channel near a site of linkage in communication between the supply portion and the paint supply channel; and a trigger valve as an open-close valve of the paint supply channel which is disposed in the paint supply channel upstream of the site of linkage in communication. After a filling liquid is filled into the branch channel, the trigger valve (open-close valve) is opened, and the paint is supplied into the paint cartridge via the paint supply channel.