An impedance matching slug that performs an impedance matching process in a waveguide is axially movably interposed between an outer conductor and an inner conductor of the waveguide. The impedance matching slug includes: a cylindrical first part and a cylindrical second part which are coupled to each other, wherein each of the first part and the second part has an inner circumferential surface facing the inner conductor and an outer circumferential surface facing the outer conductor, wherein the second part is disposed in the outside of the first part in such a manner that the inner circumferential surface of the second part is in contact with the outer circumferential surface of the first part, wherein one of the first part and the second part is constituted by a conductor, and wherein the other of the first part and the second part is constituted by a dielectric.
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