A thin film resonator having a membrane layer formed on top of a substrate, a lower electrode formed on part of the top surface of the membrane layer, a piezoelectric layer formed on top of the lower electrode, an upper electrode formed on top of the piezoelectric layer, and a mass loading layer interposed between the lower electrode and the membrane layer and having a predetermined mass. This structure enables precise adjustment of the resonant frequency of the thin film resonator, thereby providing a more precise filter.