The robot cleaner includes a main body configured to remove dust from a floor while traveling on the floor, the main body having a lateral rim defining the external appearance of a lateral surface of the robot cleaner, and at least one side brush assembly mounted to the main body to clean the corner of the floor. The side brush assembly includes a side arm pivotably coupled to the main body, the side arm moving between a first position where the side arm is inserted into the main body and a second position where the side arm protrudes outward from the lateral rim of the main body, a brush unit provided at the side arm to sweep the floor, and a rim cover coupled to the side arm to form a part of the lateral rim of the main body when the side arm is inserted into the main body.