To suppress excessive protrusion of an outer peripheral part of a diaphragm from a caulked part and stabilize characteristics of the diaphragm by caulking the outer peripheral part of the rubber elastic diaphragm by means of a support member, and embedding circular foundation cloth on the outer peripheral part of the diaphragm.

In a diaphragm device, a rubber elastic diaphragm 3 is arranged inside upper and lower cups 1, 2. A hollow chamber 4 is divided into upper and lower chambers by means of the diaphragm 3. An outer peripheral part 3a of the diaphragm 3 is caulked and fixed by means of the cups 1, 2 all over its circumference. A circular foundation cloth 6 is embedded in the outer peripheral part 3a of the diaphragm 3, that is a portion which is caulked without influence on operation and characteristics of the diaphragm 3. When the outer peripheral part 3a of the diaphragm 3 is caulked, the foundation cloth 6 is hardly extended in a planar direction compared to the elastic member. It shows shape keeping function to the elastic member, so that deterioration of the characteristics of the diaphragm 3 is prevented.