A reinforcing sleeve is a member for collectively reinforcing spliced portions of a plurality of optical fiber core wires disposed side by side. The reinforcing sleeve includes a heat-shrinkable tube, a heat-meltable member, a tension member, and so on. The heat shrinkable tube is a cylindrical member having an approximately circular cross section. The tension member and the heat-meltable member are inserted into the heat-shrinkable tube. The heat-meltable member is disposed on an upper part of the tension member. Also, an optical fiber dispersion portion is formed on a surface of the tension member on a side of the heat-meltable member in a cross section perpendicular to a longitudinal direction of the reinforcing sleeve. The optical fiber dispersion portion includes an inclined portion that is formed so as to separate away from the heat-meltable member as being closer to an end portion of a width direction in a cross section perpendicular to the longitudinal direction of the tension member.