To compactly structure a string tightening tool without using a metallic material.

The tool is constituted of a pair of sliders 10, 10, which is each provided with an elastic piece 11 projectingly on one side 14a and with an operating part 12 on the other side 14c, and a main body 20 having an operating space 21 for storing the pair of sliders 10, 10 in a slidable manner so that they are placed oppositely with the elastic piece 11 sides facing with each other. A pair of side panels 21a, 21a in the main body 20 are provided with a hole 22, 22 for putting through a string W, as are the pair of sliders 10, 10 with a hole 13, 13. The elastic pieces 11 of the pair of sliders 10, 10 are provided so that one may be superposed on the other. The main body 20 is equipped with a guide face 23 for elastically deforming the elastic pieces 11 when the pair of sliders 10, 10 are slid in the direction approaching each other.