To make it lighter and to improve its earthquake resistance, and to reduce a manufacturing cost and to make execution easier and an execution period shorter, in a column base structure having a composite construction of steel and concrete.

A cylindrical steel shell 2 composed of a steel pipe and a steel frame is erected on a foundation 6, and a cylindrical fabric bag 3 is provided along the axis of the steel shell 2 inside it, and a light filler 4 such as a light (aerated) concrete, sand, a wind broken slag is filled up in the bag 3. The concrete 5 is filled up in a space formed between the bag 3 having the filled up light filler 4 and the steel shell 2. Thus a composite column base structure 1 where a column composed of the light filler 4 is formed in a central part is constructed.