To provide a foundation for a columnar structure shortening the site work term, reducing the work execution man-hours, and having excellent excutable properties of work, and to provide its work execution method.

This foundation comprises a plurality of for example, two- divided frame precast concrete frame 16, the columnar structure 14 inserted in the precast concrete frame 16 and erected on the ground, and a concrete 28 placed between the precast concrete frame 16 and the columnar structure 14. The precast concrete frame 16 is provided with grid-shaped reinforcement 44 in its inside and anchor bolts 24 fitted and projected to an insert member 18 embedded in its inside in an opened state.