This circularly polarized wave generator comprises: a
hollow waveguide (10), one end of which is a first input / output terminal (11), the other end of which is a second input / output terminal (12), and which has a hollow part having a circular cross-section; and a pair of ridges (20), (30), each of which has a central axis parallel to the tube axis of the
waveguide (10) and which is disposed so as to face each other on the inner wall surface of the
waveguide (10). The pair of ridges (20), (30) each have a first input / output end section (21), (31) at one end section, a second input / output end section (22), (32) at the other end section, and an intermediate section (23), (33) between the first input / output end section (21), (31) and the second input / output end section (22), (32). The intermediate sections (23), (33) are periodically provided in the tube axial direction of the
waveguide (10), and each have, in a first plane perpendicular to the tube axis of the waveguide (10), a plurality of protrusions (23a1) to (23aN), (33a1) to (33aN) protruding along a line orthogonal to a line connecting the pair of ridges (20), (30), and connecting parts (23b1) to (23bN-1), (33b1) to (33bN-1) connecting protrusions adjacent at the plurality of protrusions (23a1) to (23aN), (33a1) to (33aN).