the main body includes: a substantially cylindrical socket; and a plug to be inserted into the socket to be engaged with the socket,

the socket has: a string opening for the string ends to be inserted therein; a plug opening for the plug to be inserted therein; an accommodation section for accommodating a predetermined length of the string ends inserted from the string opening, the accommodation section being in communication with the string opening and the plug opening; and a plurality of holding sections for holding the string ends accommodated in the accommodation section,

one of the socket and the plug is provided with a pair of pressing legs capable of being widened toward the holding sections to press the string ends to the holding sections, a slit being provided between the pair of pressing legs, and

the other of the socket and the plug is provided with at least one widening section that enters into the slit to urge the pressing legs toward the holding sections as the plug is inserted,

the plug has a base, said base engaging the plug opening when the string ends are accommodated in the socket such that the accommodating portion is not in communication with an exterior of the socket through the plus opening, and either one of the pressing legs or the widening section being integrally extended from the base, and

the socket and the plug each having a mating engagement portion, the mating engagement portions engage each other when the pressing legs are engaged toward the holding section and are kept widened, and the mating engagement portions preventing the plus from being disengaged from the socket.