An automatic cleaner includes a casing including a suction port, a suction device disposed in the casing to suction a foreign substance through the suction port, a moving device that moves the casing, and a side brush assembly movably installed on the casing. The side brush assembly includes a brush housing rotatable about a first rotation shaft, and a brush rotatably mounted on the brush housing by a second rotation shaft. The second rotation shaft is moved according to a rotation of the brush housing.