PURPOSE: To aim at the promotion of lightweightiness in a flap, by installing a reinforcement rib, which heightens deformability force in an axial direction of the flap, inplural spots on the outer circumferential surface, in case of the flap being attached to a space between an inner tube of a tubed tire and a rim.

CONSTITUTION: A flap 1 is made up of installing two reinforcement ribs 9 in a position where an outer circumferential surface of the flap 1 is trisected, besides installing a valve pad reinfroced part 3 in the vicinity of a valve hole 2 as in the past. These of the reinforced part 3 and the reinforcement ribs are formed into almost uniform uniform thickness at a central part of the outer circumferential surface of the flap 1, while at both sides of the flap 1 beubg expanded in tis diameter little by little, it is formed as decreasing its thickness in proportion as being approached to the side edge. According to the flap 1 like this, deformability in an axial direction is improvable over almost the whole circumference of the flap 1 and, what is more, the promotion of tinness in other parts can be set forward.