To obtain an existing conduit repairing method which can simply and certainly eliminate the gap between an existing conduit to be repaired and a regenerating conduit and can ensure stable good installation conditions of the regenerating conduit in the existing conduit.

The method comprises the intermediate member installing process wherein, before introducing the regenerating conduit into the existing one, the cylindrical intermediate member 12 having deformability that deforms at least in response to at a pressure is interposed so as to fill the gap between the regenerating conduit (14, 20) and the existing conduit 10 without interspace. By this, the gap between the regenerating conduit (14, 20) and the existing conduit 10 is filled with the cylindrical intermediate material 12 and the gap is lost certainly and simply. Thereby, the installation of the regenerating conduit free of cavity with high stability becomes possible.

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