To provide a building foundation structure and a building foundation construction method, which lowers the ratio of a foundation construction cost to total building costs, even if a building is constructed on soft ground, and which prevent the occurrence of the uneven settlement and inclination of the building over a long time.

A foundation pile 3, the upper end of which is joined to a concrete foundation 2, is driven into the ground E immediately below the position of the center G of gravity of the whole building including the concrete foundation 2 laid on the lower section of a building body 1, so that the center of gravity of the building can be supported by the foundation pile 3.