In a thin rotationally polarized antenna which performs highly reliable and highly secure wireless communication, in the case where a feeding point is provided in an integrated plate conductor including a plurality of minute conductor segments and is excited at a first frequency and a second frequency different from the first frequency, matching with a feeding circuit is achieved in both a frequency band including the first frequency and a frequency band including the second frequency. Current distribution formed in orthogonal directions on the plate at the first frequency has the same amplitude and has a phase difference of 90 degrees. Current distribution formed in the same orthogonal directions on the plate at the second frequency has the same amplitude and has a phase difference of 90 degrees, and a phase of the current distribution at the first frequency and a phase of the current distribution at the second frequency have opposite directions.