To provide a directional diversity antenna system and a communication device in which directivity is remarkably changed and an antenna gain is great.

Paired microstrip patch antennas 2, 3 are disposed at an interval on the same plane. While inverse phase side power feeding parts 72, 73 are connected to an external high frequency circuit 14 by a switching operation of a switch circuit 6, vertically polarized electric fields of mutually inverse phases are induced in the microstrip patch antennas 2, 3, thereby obtaining strong directivity in an end fire direction. While common-mode side power feeding parts 82, 83 are connected to the high frequency circuit 14 by the switching operation of the switch circuit 6, vertically polarized electric fields of the common mode are induced in the microstrip patch antennas 2, 3, thereby obtaining strong directivity in a broad side direction. In accordance with changeover of the switch circuit 6, directivity of a synthetic electric field of the microstrip patch antennas 2, 3 is changed.