To easily manufacture a patient side edge part of a mask, by mounting an almost oblong ellipse-shaped mounting member on the patient side edge part of a tube, and circularly mounting a cylindrical member made of a soft material, on a peripheral edge of the patient side edge part in such manner that a circular cuff is formed.

A flexible tube 1 is made of a plastic material such as polyvinyl chloride, and a coupling 10 is mounted on an edge part 12. The tube 1 includes the lumen for expansion, in a wall, and is extruded and molded. A mask part 13 including a comparatively hard plastic mounting member 15, is formed on a patient side edge part 14 of the tube 1. That is, the oblong ellipse shaped or egg-shaped outer edge part which has a recessed notch part 19 having the shape of an inverted plate, is formed on the patient side edge part 18 of the mounting member 15. Then the expansible cuff 25 formed by an almost cylindrical member 30 made of a soft material such as polyurethane, is mounted on the same through a mounting plate 26. Whereby the patient side edge part can be easily manufactured.