There is disclosed a method of aligning an azimuth of an antenna by use of an antenna azimuth aligning instrument capable of economically and precisely aligning the azimuth in a case where a direction of a main beam of a directional antenna is matched with a counter antenna. There is provided a method of aligning the azimuth of the directional antenna by use of the antenna azimuth aligning instrument to be attached to the antenna for use in radio communication, the azimuth aligning instrument includes an aiming hole whose central axis is constituted in parallel with a main beam azimuth of the antenna and in which a diameter of an opening 2C on an operator's viewing side is set to be larger than that of an opening 2B on a target side, and the azimuth of the antenna is aligned using the centers of the two openings of the aiming hole as aims for a target.