The present invention particularly relates to a foundation body and method of disposing additional reinforcing materials in foundations formed with a reinforced base which obtains a high underpinning strength with respect to detaching loads. The natural ground 4 is excavated. A plurality of rod shaped additional reinforcing materials are fixed in the peripheral earth which extend radially from the formed main foundation body and which are disposed at fixed intervals in the radial direction. The additional reinforcing materials are disposed so as to be corresponded with the direction of minimum principal strain in the earth peripheral with respect to the foundation body when a detaching force acts.