PURPOSE: To improve strength, heat resistance, and a propagation velocity, to facilitate the setting of an elastic modulus, and to obtain a diaphragm with superior characteristics, by using inorganic fiber as a raw material for paper working.

CONSTITUTION: A wire cloth in a prescribed shape to be formed, e.g. corn shape is set in a paper making vessel 1. Inorganic artificial fiber such as carbon fiber and glass fiber 4 is dispersed uniformly a dilute suspension 3 by using a surface active agent and zirconia colloid is mixed therein as a binder 5. The zirconia collid and water-soluble thermosetting resin are used in common as the binder 5. A reinforcing material for improving the strength of a diaphragm more uses a silicon nitride whisker, etc., together with the inorganic fiber. An original diaphragm shape 6 made with the wire cloth 5 is pressed thermally at, for example, 150∼160°C by heat process devices 7 and 7' to vaporize the water in the fiber. The dried original diaphragm shape is put in a heating furnace 8 and cured thermally at about 300°C, obtaining the speaker diaphragm 9.