A mobile robot measures a rotation angle using information from an image photographed by a vision camera. A mobile robot system comprises a main body of the robot, a driving part for driving a plurality of wheels; a vision camera mounted on a main body thereof to photograph an upper image which is perpendicular to a traveling direction; and a controller for calculating a rotation angle using polar-mapping image data obtained by polar-mapping a ceiling image, photographed by the vision camera, with respect to a ceiling of a working area. The controller drives the driving part using a calculated rotation angle. The rotation angle is measured by the vision cameras and the rotation angle can be used to compensate the working path, without having to provide expensive devices such as an accelerometer or a gyroscope, thereby saving manufacturing cost.