To provide a repair structure of an existing collection drainage pipe, capable of easily and surely suppressing propagation of iron bacteria inside the existing collection drainage pipe buried underground, making clogging in the existing collection drainage pipe hard to occur, and maintaining an excellent collection drainage performance over a long period of time even while reducing the maintenance of the existing collection drainage pipe.

In the repair structure of the existing collection drainage pipe, a porous pipe 10 for repair provided with a plurality of water permeating holes 10a.. and also provided with an antibacterial agent 11 at least on the outer peripheral surface side is inserted into the existing collection drainage pipe 1 buried underground to attain a double structure, and the propagation of iron bacterial in a gap S between the existing collection drainage pipe 1 and the porous pipe 10 for the repair is suppressed by the antibacterial agent 11 on the outer peripheral surface side of the porous pipe 10 for the repair.