Abstract: A fastening device is structured so that one half thereof is symmetrical with the other and includes a casing, with a pair of inwardly folded portions, and a pair of symmetrical block-members, each having a bar-member and accommodated within the casing such that one end of each block-member is respectively outwardly biased toward the lateral open ends of the casing. Respective end portions of strings or the like are wound around the respective bar-member and respectively abut the respective folded portions as long as the respective ends of the block-members remain outwardly biased and are not pushed inwardly by a user.