A tunable bandpass filter (1A) includes a waveguide (11); a plurality of resonators (12) housed in the waveguide (11) and arranged in the lengthwise direction of the waveguide (11); a coupling member (13) disposed between two adjacent resonators (12); a ridge member (14) extending in the lengthwise direction of the waveguide (11) and connected to one end of the coupling member (13); and a dielectric plate (17) extending in the lengthwise direction of the waveguide (11), disposed adjacent to the plurality of resonators (12) in a direction orthogonal to the lengthwise direction of the waveguide (11), and movable in the direction orthogonal to the lengthwise direction of the waveguide (11).