A radio wave receiving converter includes a main body portion including a first waveguide having a male thread on an outer circumference of the first waveguide, a feedhorn including a second waveguide having a female thread on an inner circumference of the second waveguide, a ring-shaped member including a circumferential wall portion and an annular step portion such that a groove portion where a portion near a tip of the second waveguide is inserted between the ring-shaped member and the outer circumference of the first waveguide is formed, and a sealing agent injected into a groove portion "b". By this configuration, there is provided a radio wave receiving converter that has a simple structure of a connecting portion, has improved productivity of the components and assemblability of the finished components, and can achieve a reduction in size and weight.