To provide a subdrainage treating material for civil engineering that prevents a gap from being formed at a joint to avoid cutting of a headrace to thereby prevent such an accident that water flowing through the headrace overflows from the joint.

At least one end in the longitudinal direction of a treating material body 1 formed into a band shape and having a fixed length, and the end of an adjacent treating material body 1a abutting on the one end, include an engaging part 18 and an engaged part 19 engaged with each other to connect the treating material bodies 1, 1a so as to prevent a gap from being formed at the joint.