To improve yield in the manufacturing method of a thin-film resonator forming a cavity by using a sacrifice layer.

A solution including dielectric 4a is coated on the surface of an Si substrate 1 including a recess 3 by a spin-on, and then a spin-on film 4 is formed. The coated dielectric 4a is sintered with heat processing. At that time, by adjusting a thickness of a solution coated so that the thickness of the dielectric 4a after sintering may be the same depth of the concave 3, the recess 3 is filled with the dielectric 4a (sacrificing layer) and the surface of the Si substrate 1 is smoothed without using mechanochemical processing like chemical mechanic polishing.