PURPOSE: To improve strength for a reinforced concrete structure by a method wherein rapid drying of concrete is prevented when the structure is built up, and the concrete is made to stick fast to and integrate with the reinforcements.

CONSTITUTION: Weathering film on the exterior of reinforcements is scoured off with the reinforcements turned in a scouring sand box, and the reinforcements are used with their original exterior exposed after scouring. Round steel bars 6, each equipped with a handle, are erected between the reinforcements 2 on necessary positions in concrete. After placing of concrete 1, the handles are turned quickly, making cementation to the concrete 1 prevented. After initial hardening, the round steel bars are extracted, and thereby water supply holes 7 are formed and water supply channels 8 are formed at the surface of the concrete 1. With water supplied to the water supply holes 7, the concrete 1 can be prevented from becoming dry quickly. After hardening of the concrete is completed, the water supply holes 7 are sealed up with the reinforcements 2 and mortar concrete.