To provide a simple and inexpensive concrete repair material injection plug having a small outside diameter and suited for disposal.

The plug includes an end injection plug 11 formed of a cylinder with a small outside diameter; a root injection pipe 12 formed of a cylinder with a large outside diameter which can be mounted at the root of the end injection pipe 11; an elastic cylinder 13a surrounding the outer peripheral surface of the end injection pipe 11; a fixing mechanism 13 comprising compression mechanisms 13b and 13c for pressing the elastic cylinder 13a against the interior wall surface of an injection hole by compressing the cylinder in a direction parallel to its axis to cause radial expansion of the cylinder, for fixing the elastic cylinder 13a into an injection hole; and a backflow prevention mechanism 14 formed inside the root injection pipe 12.