To provide a restraining device capable of accurately and easily restraining the insertion length thereof after the installation in a drain pipe facility in which the insertion length of a lower end straight pipe part when the lower end straight pipe part is inserted and connected to an upper socket is restrained to a given length.

This restraining device comprises a socket outer fitting part 52 fitted to the outside of the upper socket 26 of a drain rising pipe 30, a positioning means 56 for restraining the axial position of the socket outer fitting part 52 relative to the upper socket 38 of the drain rising pipe 30, an insertion restraining part 54 formed in a cylindrical shape shorter in length than the lower end straight spigot 26 for guiding the lower end straight spigot 26 to the upper socket 38 by inserting the lower end straight spigot 26 of a drain pipe fitting 20 thereto and restraining the insertion length L1 of the lower end straight spigot 26 by bringing the upper end of the cylindrical shape into contact with the lower end 25 of the body part 22 of the drain pipe fitting 20. The lower end straight pipe part 26 and the upper socket 38 are detachable and attachable in the connected state.