PURPOSE: To improve the acoustic characteristic of a flat diaphragm in which a core member and a surface member are adhered by using additionally a film of a polyamide resin or polyamide copolymer resin having ≤5% of water absorption in water at 20°C.

CONSTITUTION: The flat diaphragm consists of a foamed body, core member made of a honeycomb member and a surface member made of a metal foil or a plastic film by adhering them. The film made of a polyamide resin or a polyamide copolymer resin having ≤5% of water absorption in water at 20°C is laminated to the surface member of the flat diaphragm.