An easy-to-fabricate and relatively strong circularly polarized loop antenna of a simple construction is built. A circularly polarized loop antenna 1 has a loop section 11, which is made up of a loop-shaped conductor whose length is equal to 1 wavelength (λ) of the transmitted and received signals, and a coupling section 12, made up of a conductor, is connected thereto at a prescribed point. The coupling section 12 is shaped such that it is connected to the loop section 11 at a connection point 201 at one end and extends along the loop section 11 throughout a length equal to λ/4. A reflective plate 2 is placed in a predetermined position in the vertical direction from the circumferential plane of the loop section 11, in parallel to the circumferential plane. In addition, the other end of the loop section 11 is connected to external circuitry carrying out the processing of signals transmitted and received via a first feed conductor 13 and a second feed conductor 14 and operates as a feed point, 200.