Waveguide coaxial converter

Disclosed is a waveguide coaxial converter which has a waveguide which is in the form of a bottomed rectangle and in which a high-frequency signal propagates; at least two means for regulating a capacitive susceptance which are provided with having a predetermined angle to an axis line of the waveguide at a predetermined position on a wide face of the waveguide and are respectively disposed at an interval of one eighth of a guide wavelength lambda g in the direction of the axis line; and at least a pair of step portions for stepwise narrowing the width between both internal sidewalls of the waveguide, each of the step portions being provided on the internal sidewalls respectively, wherein the step portions are placed with a distance of one eighth of the guide wavelength in the direction of the axis line.