A piston, which is displaceable by pilot air, is provided in a main body. A valve plug, which is composed of a resin material, is connected to an end of a shaft connected to the piston. The valve plug is seated on a valve seat section of a sub-body connected to the main body, and thus the flow of the paint to a flow passage is cut off. A seating section of the valve plug, which is to be seated on the valve seat section, is formed to be substantially spherical. Further, the surface of the valve seat section is recessed and substantially spherical corresponding to the seating section.