A circularly polarized wave antenna which allows the matching of resonant frequencies in a higher order mode to be easily achieved. In this circularly polarized wave antenna, a flat portion is provided by flattening a portion of the peripheral side surface of a substrate. Two feeding electrodes for use in the higher order mode excitation are formed on this flat plane. On one main surface of the substrate, a circular radiation electrode is formed, while, on the other main surface of the substrate, a ground electrode is formed.