To provide a segment surely and efficiently cutting off water by injection of a necessary minimum amount of cut-off material when the water leaks by crack and the like of a joint surface between segments in the segment comprising a tunnel lining constructed on a tunnel excavation wall surface.

This segment is so formed that inner/outer two seal materials 4 and 5 are endlessly installed across the whole circumference of the end face of a segment body 1 and partitioning seal materials 7 connecting the seal materials 4 and 5 are installed in the respective end faces of the segment body 1. The segments are mutually joined by joining the opposed end faces together so that the seal materials 4 and 5 and the partitioning seal materials 7 and 7 are brought into press contact, clearances 8 between the opposed end faces are hermetically sealed by the seal materials 4 and 5 and the partitioning seal materials 7 and 7. This constitution prevent the seal materials from entering and diffusing in the clearances, other than the clearance 8, in the segment circumferential direction and allows the seal materials to fill only the clearance 8.