PROBLEM TO BE SOLVED: To provide a sheath tube capable of securing airtightness for a long period of time.SOLUTION: A sheath tube 100 according to the present invention includes two insertion holes 168 and 170 to insert an insertion part 12 of an endoscope 10 and an insertion part 52 of a treatment tool 50. The insertion holes 168 and 170 are so formed that a distance (a) from a center C1 of the insertion hole 168 to a wall core of a partition wall 172 is shorter than a distance b from the center of the insertion hole 168 to an edge in an opposite side of the partition wall 172, and the distance (a) from a center C2 of the insertion hole 170 to the wall core of the partition wall 172 is shorter than the distance b from the center C2 of the insertion hole 170 to the edge in the opposite side of the partition wall 172.SELECTED DRAWING: Figure 14【課題】本発明は、気密性を長期にわたって確保できる外套管を提供する。【解決手段】本発明の外套管１００は、内視鏡１０の挿入部１２と処置具５０の挿入部５２を挿通する二つの挿通孔１６８、１７０を備える。挿通孔１６８、１７０は、挿通孔１６８の中心Ｃ１から隔壁１７２の壁芯までの距離ａが、挿通孔１６８の中心から隔壁１７２と反対側の縁部までの距離ｂよりも短く、挿通孔１７０の中心Ｃ２から隔壁１７２の壁芯までの距離ａが、挿通孔１７０の中心Ｃ２から隔壁１７２と反対側の縁部までの距離ｂよりも短く形成される。【選択図】図１４
