PURPOSE: To obtain a speaker with superior characteristics which make the most of merits of a compound structure diaphragm by forming a composition transition layer which has slow transition on the boundary surface between a base made of metal and a surface high-rigidity ceramic layer.

CONSTITUTION: The metal used for the base 1 of the diaphragm 1 is formed in a diaphragm shape and the composition transition layer 2 is formed of a compound of oxide ceramic and base metal by a physical vapor deposition (PVD) method. The high-rigidity ceramic layer 3 is formed on the surface of the transition layer 2 by the PVD method. Consequently, a diaphragm which has density ρ nearly equal to that of the metal layer of the base 1, a Young's modulus E nearly equal to that of the ceramic, and extremely large specific strength E/ρ is obtained. Further, the transition layer 2 is formed of the compound of the base metal and surface ceramic, so it combines with both layers in extremely close contact and the cracking and separation of the ceramic layer are eliminated completely.