To provide, at a low price, a string fastening implement made of synthetic resin, which is manufactured from economical material, presentable in appearance, has an excellent strength for greatly reducing damage, prevents a fastening string from injuring, and achieves a superior fastening function with a shorter full length.

A string fastening implement is constituted so as to catch a fastening string 4 through differential force of a compression coil spring 3 between an opening rim of a piercing hole 4 of an outer cylinder 1 having a hole H on the bottom, and an opening rim of a string inserting hole 9 of an engaging piece 2 moving up and down inside. In this case, the string inserting hole 9 for inserting both of the fastening string 14 and a pulling string 11 is pierced horizontally on the engaging piece 2 of a column shaped part 7. And on the lower part of the column shaped part 7, a protrusion piece supported by a spring 8 is formed unitedly, which serves also as reinforcement. On both of the opening rims of the string inserting hole 9, a groove for subsiding a string 9a is formed. The pulling string 11 inserted into the string inserting hole 9 is put into the groove for subsiding a string 9a to make it uniform, and the compression coil spring 3 is mounted to unite with the outer cylinder 1.