This disclosure provides a waveguide converter, which includes a first waveguide for propagating an electromagnetic wave, a second waveguide for being inputted the electromagnetic wave from the first waveguide and propagating the electromagnetic wave in a direction different from the propagating direction of the electromagnetic wave in the first waveguide, and an elongated-plate-shaped inner conductor arranged between the first waveguide and the second waveguide so that end portions of the inner conductor are exposed to the inside of the first waveguide and the second waveguide, respectively.