To provide a circularly polarized antenna capable of obtaining an excellent axial ratio over a very wide range and having a great gain in a zenith direction. The circularly polarized antenna (10) includes a planar loop antenna element (122) and feeding means for providing quadruple feeds with their phases varied by 90 degrees with respect to the planar loop antenna element (122). The feeding means has four feeding probes (131 through 134). The circularly polarized antenna (10) is provided with a circuit board (25) disposed in parallel with the planar loop antenna element (122). The circuit board (25) has an area greater than that of the planar loop antenna element (122). The circuit board (25) has a principal surface (25U) which entirely serves as a ground plane. The circuit board (25) has a rear surface (25L) provided with a 90-degree phase shifter formed thereon.