A suction nozzle which when being stopped up automatically delimits the suction force in the suction opening (2) to a certain predetermined value independently of the negative pressure in the suction conduit (1, 12). The suction nozzle comprises a sleeve member (3) arranged at the front end of the suction conduit (1, 12) and which forms the suction opening (2) of the device. The sleeve member (3) is by a resilient member (4) held in a first position, suction position, in which it covers side passages (5.6;15) to the suction conduit (1) and in which suction is performed through the suction opening (2). If the pressure difference immediately inside and outside the suction opening (2) exceeds a certain value, e.g. if the suction opening is stopped up, the sleeve member (3) is against the action of the resilient member (4) automatically displaced to a second position in which said side passages (5,6;15) to the suction conduit are opened, thereby reducing the suction force in the suction opening (2).