fig9 a 9 c and fig1 fig9 a shows the knitted textile member 23 constituted by a tubular knitted textile the knitted textile member 23 has a stitched portion which are hardened by impregation of a resin not to expand even if the tube 22 inserted inside thereof is inflated a resin coating 23c indicating a weak tackiness is provided onto the knitted textile member 23 so that the stitches of the knitted textile member 23 can not be expanded when the belt is pulled during normal wearing as the tube 22 is inflated by the introduced gas and then the gas pressure is applied the adhesive of the resin coating impregnated into the stitches is broken so that the inflatable portion is inflated promptly since the both side portions 23a having strong resin coatings are not deformed and remain as they are even when the tube is inflated only the gas path portion is inflated in a slender cylindrical shape also in this altered example an inflation shape similar to the state shown in fig8 is accomplished further according to the altered example the inflatable range can be controlled by the knitted fabric per se and the cover 20 can be omitted since the stitches do not expand during normal wearing because of the weak resin coating fig9 b shows an altered.