In a diaphragm of an electric sound converter which converts vibration such as sound into an electrical signal, a center dome is reinforced while suppressing variations in the sensitivity and frequency response to the minimum, whereby reduction in a high-pass reproduction limit is suppressed, and occurrence of anomalous resonance is prevented. In a diaphragm 1 of an electric sound converter having a center dome 2, a reinforcing film 7 made of the same material as that of the center dome and formed into the same shape as that of the center dome is applied to the center dome with a hot-melt adhesive 6 of the same nature as that of the center dome, a groove 7a formed in a polygonal reticulate pattern is provided on one surface of the reinforcing film adhered with the adhesive, and a convex rib 8 corresponding to the groove is formed on the other surface.