<p>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 barmember 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.</p>
