A robot according to the present invention cleans the outer surface of a window/wall by performing automatic movement along the outer surface of the window/wall while being vacuum-sucked onto the outer surface. The robot includes a moving unit for moving the robot in a first direction, a direction changing unit for rotating the moving unit to change a movement direction of the robot, and a cleaning unit mounted on at least one side of the robot. The robot can prevent water used to clean the window or outer wall of a building from being dropped toward a lower story. Also, the robot can run smoothly so that it can achieve a satisfactory cleaning operation without forming spots. The robot uses a turntable system, so that it can also freely change the movement direction thereof about the center thereof up to 360° without requiring any radius of rotation, to easily approach even a dead zone. The robot has a minimum size and a minimum weight, so that it can minimize the possibility that the robot falls down during a cleaning operation.