In one exemplary embodiment, a second waveguide is connected to an upper wall of a first waveguide and communicates with the first waveguide, a dielectric window is in contact with a lower wall of the first waveguide, a first inner conductor penetrates an upper wall, is electrically connected with the upper wall, and extends along the direction of a tube axis from an inside of the first waveguide to an inside of a third waveguide, the third waveguide is connected to the lower wall on the dielectric window side and communicates with the first waveguide, a first opening end of the third waveguide is connected to the dielectric window, and a drive device is connected to the first inner conductor, and is configured to drive the first inner conductor in the direction of the tube axis.