A reinforcement sleeve is a member for reinforcing a connection part of an optical fiber tape core wire, and comprises a heat-shrinkable tube, a heat-meltable member, a tension member, and the like. The heat-shrinkable tube is a cylindrical member. The tension member is a rod-shaped member. The tension member and the heat-meltable member are inserted in the heat-shrinkable tube. The heat-meltable member is disposed above the tension member. The tension member is approximately circular or approximately elliptical in a cross section perpendicular to the longitudinal direction of the reinforcement sleeve. More specifically, the surface on the heat-meltable member side of the tension member is formed to have an arc-shaped convex curved surface in a cross section perpendicular to the longitudinal direction of the tension member.