A reinforcement sleeve for connecting a plurality of optical fibers to each other by fusion splice includes: a base member; a cover member that sandwiches a fusion splice portion of the plurality of optical fibers between the cover member and the base member; a first adhesive layer disposed between the base member and the plurality of optical fibers; and a second adhesive layer disposed between the cover member and the plurality of optical fibers. A width of the reinforcement sleeve is defined by a reinforcement sleeve standard relating to a reinforcement sleeve, and a height of the reinforcement sleeve is 1/n of a height defined by the reinforcement sleeve standard, where n is an integer equal to or larger than 2.