An acoustic resonator includes: a substrate; a resonant portion including a center portion in which a first electrode, a piezoelectric layer, and a second electrode are sequentially stacked on the substrate, and an extension portion disposed along a periphery of the center portion; and a first metal layer disposed outwardly of the resonant portion to be electrically connected to the first electrode. The extension portion includes a lower insertion layer disposed on an upper surface of the first electrode or a lower surface of the first electrode. The piezoelectric layer includes a piezoelectric portion disposed in the center portion, and a bent portion disposed in the extension portion and extended from the piezoelectric portion at an incline according to a shape of the lower insertion layer. The lower insertion layer is formed of a conductive material extending an electrical path between the first electrode and the first metal layer.