A piezoelectric thin film resonator includes: a piezoelectric film provided on a substrate; a lower electrode and an upper electrode sandwiching at least a part of the piezoelectric film and facing with each other; and an inserted film that is inserted in the piezoelectric film, is provided in an outer circumference region of a resonance region and is not provided in a center region of the resonance region, wherein: an angle between an edge face of the lower electrode and a lower face of the lower electrode in the resonance region is an acute angle; and a width of the inserted film in the resonance region on a side for extracting the upper electrode from the resonance region is larger than another width of the inserted film in the resonance region on a side for extracting the lower electrode from the resonance region.