PURPOSE: To make the rigidity of a diaphragm large and to improve the fragility and shock resistance by specifying carbon fiber in a diaphragm member made mainly of a layered mineral in which a curing agent or a curing accelerator is adsorbed between layers, thermosetting resin monomer and carbon fiber.

CONSTITUTION: The member is made by heating and forming main materials consisting of a layered mineral in which a curing agent or curing accelerator is adsorbed between layers, a thermosetting resin monomer and carbon fiber. The carbon fiber of relatively short fiber length, 30∼1,000μm, and that of relatively long fiber length, 3∼8mm, are used jointly. In a diaphragm of such constitution, a montmorillonite-epoxy composite is dispersed so as to fill the spaces of carbon fiber of relatively short fiber length and carbon fiber of relatively long fiber length and bonded to each other. Accordingly, the bending strength is increased, the weak fragility is improved and the shock resistance can be heightened.