PURPOSE: To attach a covering body on a cut part of an existing duct accurately by moving a covering body inside the existing duct in the condition of being supported by an expansion body of an enlargement means and attaching the covering body inside the existing duct after enlarging it by means of expanding an expansion body in the radial direction.

CONSTITUTION: An attaching device 10 is passed through a covering body 14 and pressure fluid is supplied between the outer surface of a supporting body 32 and the inner circumferential surface of an expansion body 36 causing the expansion body 36 to expands and the covering body 14 to be arranged in a recess 44 of the expansion body 36. The application device 10 is then moved inside an existing duct 12 up to a cut part 16 and further moved after moving both sliders 54 to the outside of the radial direction of the supporting body 32 and pushing an end portion 62a of an engaging portion 62 against the inner surface of the existing duct 12. Because the covering body 14 and the cut part 16 are forced in position when the end portion 62a of the engaging portion 62 engages with an end edge 44a of the recess 44, pressure fluid is supplied between the outer circumferential surface of the supporting body 32 and the inner circumferential surface of the expansion body 36 causing the expansion body 36 to be pushed against the inside wall surface of the existing duct 12 and deform a sleeve 74 by compression.