PURPOSE: To improve sealing property and to prevent the invasion of foreign substances by a method wherein a circular disc type non-return valve, effecting air suction, is provided with a sealing part and a recess, which is provided at the inside of a valve body, to permit point contact respectively and prevent the invasion of the valve body into a suction hole by thickening the thickness thereof.

CONSTITUTION: The circular disc type non-return valve 70, effecting air suction in accordance with the pressure difference between the pressure of an air chamber (not shown in the diagram) and an atmospheric pressure, is consisting of a circular disc type valve body 71, the sealing part 72, provided with a protuberance having the tip end of an acute angle at the periphery of the valve body 71 and a stopper 74 formed on a valve rod 73 so as to have a diameter larger than the same of the valve rod 73 while the valve is formed integrally by an elastic body. The sealing part 72 is contacting through the point contact, therefore, the thickness of the valve body 71 may be made thicker than the thickness of the valve body of a conventional ambrella-type suction valve, the valve body 71 will never invade into the air suction hole 14 and the sealing property may be improved. Further, the recess 77 is provided at the inside of the valve body 71 to contact it through point contact, therefore, the foreign substances may be removed upon opening the valve even if they are invading from the outside thereof.