Realized is a post-wall waveguide bandpass filter in which a bypass phenomenon is less likely to occur. In a post-wall waveguide bandpass filter (1) including an input part (10a) and an output part (10b), an external post wall (14a1, 14a2, 14b1, 14b2) is provided which is constituted by at least one conductor post that is provided outside a waveguide region (D1) and that short-circuits an outer periphery of an upper wide wall (12a) and an outer periphery of a lower wide wall (12b).