An acoustic resonator includes a substrate, and a resonant portion comprising a center portion in which a first electrode, a piezoelectric layer and a second electrode are sequentially laminated on the substrate, and an extending portion disposed along a periphery of the center portion, wherein the resonant portion is configured to have an asymmetrical polygonal plane, an insertion layer is disposed below the piezoelectric layer in the extending portion, and the piezoelectric layer is configured to have a top surface which is raised to conform to a shape of the insertion layer, and the insertion layer is configured to have an asymmetrical polygonal shape corresponding to a shape of the extending portion.