PURPOSE: To establish a grout injecting method to the back face of a concrete structure by which grout can be injected certainly to the back face ground and an injection hole can be formed at a low cost.

CONSTITUTION: A concrete structure 2 is built by installing internally a guide pipe 6 for grout injection, and a grout injecting pipe 8 is inserted through the guide pipe 6, followed by injection of grout 4. A crack is generated in a specified place on the back face of the structure with the grout injecting pressure from a guide pipe jetting hole 6a so that a gout injection path leading to the back face ground 3 is provided, and then the grout 4 is injected into the ground 3. There is no need to excavate the body or ground 3 after building of the structure owing to the guide pipe 6 or grout injecting pipe 8, and accurate injection into the ground 3 can be performed. In the guide pipe 6, a plurality of above-mentioned injection holes 6a are provided in the longitudinal direction, and it is made practicable to make grout injection to different depths using the same pipe 8 with injection hole by changing the inserting position of the pipe 8.