A producing method for a diaphragm-type resonant MEMS device includes forming a first silicon oxide film, forming a second silicon oxide film, forming a lower electrode, forming a piezoelectric film, forming an upper electrode, laminating the first silicon oxide film, the second silicon oxide film, the lower electrode, the piezoelectric film, and the upper electrode in this order on a first surface of a silicon substrate, and etching the opposite side surface of the first surface of the silicon substrate by deep reactive ion etching to form a diaphragm structure, in which the proportion R2 of the film thickness t2 of the second silicon oxide film with respect to the sum of the film thickness t1 of the first silicon oxide film and the film thickness t2 of the second silicon oxide film satisfies the following condition: 0.10 μm≦t1≦2.00 μm; and R2≧0.70.