To provide a fashionable bag opening/closing implement which can surely and easily close the opening of the bag.

This bag opening/closing implement 1, comprising a string 2 and a clamp 3, has one end or both ends 21 and 22 of the string 2 become a loop; the clamp 3 has a cylindrical shape; the inside of its cylindrical bottom is provided in the following order starting with a bottom plate 31, an elastic body 32, a partition plate 33, a cylinder 38 connecting the partition plate 33 to a button 36, and the button 36; the sidewall of the clamp 3 in its upper part, is provided with two small windows 37 and 37 having projecting parts 39 and 39; the string 2 passes through the two windows and is positioned between the partition plate 33 and the button 36; a substantially U-shaped window 34, having downward projection 35 at its center, is provided in the sidewall opposite to the two small windows 37 and 37; and the loop 21 or 22 is locked to the projection 35.