The present invention relates to a diamond vibration plate for a speaker having high sound velocity or E/.rho. and which is superior in high-pitched tone performance. Conventional diamond vibration plates which are made overall from crystalline diamond were apt to split or break at a flange due to the high rigidity. According to the present invention periphery of the flange is circularly cut by laser beams to eliminate rugged circumference. The laser treatment also converts the crystalline diamond of the flange into non-diamond carbon. The resulting vibration plate with a central spherical part of crystalline diamond and a periphery of a flange of non-diamond carbon excels both in high frequency property and mechanical strength.