A corrugated tube mounting jig 5 for mounting a corrugated tube C, having a slit S formed in a longitudinal direction, on a wire bundle W, has a higher flexibility at its distal end portion, and has a larger restoring force at the other portion. This corrugated tube mounting jig 5 includes a folded-back portion 51 of a generally U-shape for gripping the wire bundle W, side plate portions 52 which are continuous with the folded-back portion 51, and extend to be disposed respectively at opposite sides of the wire bundle W, and are arranged parallel to each other, and have respective end edges slanting relative to the wire bundle W, and a flange portion 53 which is formed at the slanting end edges of the side plate portions, and extends outwardly of the side plate portions 52. At least that portion of the folded-back portion 51 which defines its distal end portion with respect to a direction X of insertion of the corrugated tube C is made smaller in thickness than the other portion.