A method of producing a thin film bulk acoustic resonator having a piezoelectric layer, a first electrode joined to a first surface of the piezoelectric layer, and a second electrode joined to a second surface of the piezoelectric layer, which is located at the opposite side to the first surface, including the steps of forming a pit on a surface of a substrate; filling the pit with a sacrificial layer; polishing a surface of the sacrificial layer so that the RMS variation of a height of the surface of the sacrificial layer is equal to 25 nm or less; forming the first electrode over a partial area of the surface of the sacrificial layer and a partial area of the surface of the substrate; forming the piezoelectric layer on the first electrode so that RMS variation of a height of the second surface of the piezoelectric layer is equal to 5% or less of a thickness of the piezoelectric layer; forming the second electrode on the piezoelectric layer; and removing the sacrificial layer from the inside of the pit by etching.