A tunable band-pass filter includes: a rectangular waveguide including a first and a second waveguide parts, which are acquired by dividing the rectangular waveguide along an E-plane of the rectangular waveguide at a center position of an H-plane in the rectangular waveguide; a metal plate sandwiched by the first and the second waveguide parts in such a way as to be parallel to the E-plane; at least one dielectric plate arranged in the rectangular waveguide in such a way as to extend in a longitudinal extension direction of the metal plate; and a drive mechanism changing a relative position relationship between the dielectric plate and the metal plate from the outside.