Abstract: A coating method and apparatus for coating the inner surface of a long tube of small diameter, specifically tubes for a condenser. The coating is a type of spray coating wherein a long flexible supply hose, longer than the long tube to be coated, is reciprocated in the long tube with a spray nozzle attached to the tip thereof for spraying the paint by the action of compressed air, from one end of the long tube to the other end thereof while spraying the paint in atomization. The long flexible supply hose of double structure or sometimes of triple structure is composed of a short heating pipe portion adjacent to the spray nozzle and a long flexible hose portion. The paint and compressed air supplied through separate passages in the supply hose are heated to a predetermined temperature by heating means, for example, a sheathed electrical heater wound about an inside pipe of the heating pipe portion upstream of where the paint is sprayed.