To remove surely a coating adhering to the inside of a bell head or a rotating body rotating by an air motor.

A housing 5 is connected to a double-pipe type feed tube 2 supplying air and thinner to the bell head 4 fixed to the hollow rotating body rotation-driven by the air motor, and has in the back-end surface 5a an air supply port 7 supplying only air to a hollow 51 of the housing and an air-thinner supply port 8 supplying alternately air and thinner to the hollow, which are arranged at the position offset from the circle center of the hollow. A funnel part 52 formed conically so as to be tapered toward a space 22 of the feed tube is provided on the fixed side of the hollow feed tube. An outer casing 23 of the feed tube has, on the tip opening 23a, four radially-inclined grooves 24 notched at an angle in an outer circumferential direction from the inner circumferential surface 23b toward the tip, and the tip 23d is arranged at the position in which air and thinner discharged along the inclined grooves are introduced into the inner circumferential surface 41 of the bell head along the inner circumferential surface 31 of the rotating body.