To execute insection of a rope in a short time even if a duct has an intricate curve by executing insertion of a rope into a duct by sucking a natural silk thread tied to a guide ship and replacing the tied silk with the rope by tying the silk to the rope and drawing back the silk from a starting position.

At a cleaning start point, a guide ship 5, to a trailing end part of which a natural silk thread 6 is tied, is disposed in an air supply duct 1 and a damper 2 is opened and a dust collector located at a front end side of the air supply duct 1 is operated to suck the guide ship 5 to a finish position. Then, the natural silk thread tied to the trailing end part of the guide ship 5 is untied and the natural silk thread 6 is tied to one end of a rope 7 and the guide ship 5 is lowered out of the duct, and the silk thread 6 is pulled back at the start point to draw the rope 7 near and the rope 7 is laid within the duct extending from the finish point to the start point and is stretched. Then, the rope 7 tied to the natural silk thread 6 at the start point is untied and is tied again to a drawer part of a blast cleaner 8.