PURPOSE: To completely integrate movable reinforcement with adjacent blocks by a method in which a cylindrical tube leading to an injection tube is provided between a partition plate and the injection tube provided in parallel with the partition plate, and the movable reinforcement is inserted into the cylindrical tube in a reciprocally movable manner.

CONSTITUTION: A device 3 is set in the trench 1 for forward blocks A, iron bars are set, concrete is placed and hardened, and then a trench 1' is excavated for the adjacent blocks B. A hardening agent 17 is sent under puressures from an injection inner tube 5, injected from an outlet port 8 into an outer tube 4 injection, and further directed into a cylindrical tube 6, whereupon a pressure is applied to the piston body 15 of a movable iron bar 7 and the iron bar 7 is advanced and projected from a partition plate 2. The hardening agent is filled up in the tube 6 and solidified integrally with the movable iron bar 7. Lastly, iron bars are set in the adjacent blocks B and concrete is placed to connect both the blocks A and B to construct an underground wall.