To decrease work processes and shorten the period of construction work by placing a precast concrete member of a predetermined shape on mortal laid for height adjustment and then pouring concrete after laying reinforcing bars inside.

A foundation pile 7 is poured with foundation piles 7 projected out to a predetermined length in the bottom portion of a foundation groove 6 excavated and formed and dry mortal 8 is laid to a predetermined thickness for height adjustment. After hardening of the dry mortar 8, a precast concrete member 1 is placed on the dry mortal 8 where cement paste 9 has been laid, and reinforcing bars such as column bars 12, tenon bars 13 and truss bars 14 are arranged in the precast concrete member 1 after arranging the formwork 11 for preventing the outflow of concrete to be poured later inside the foundation pile 7. Next, sediment is backfilled around the precast concrete member 1, concrete is placed inside the precast concrete member 1, and the building of the foundation is completed. By doing this, the work process can be greatly reduced, thereby shortening the period of the construction work.