An antenna device (4) includes a first phase shifter (24) having one end connected to a fourth terminal (23d) of a directional coupler (23); a second phase shifter (25) having one end connected to a first terminal (23a) of the directional coupler (23); a third phase shifter (26) having one end connected to a second terminal (23b) of the directional coupler (23); a first matching circuit (27) having one end connected to an other end of the second phase shifter (25) and having an other end connected to a first input/output terminal (11); and a second matching circuit (28) having one end connected to an other end of the third phase shifter (26) and having an other end connected to a second input/output terminal (12).