In a column structure, a steel column having flanges integrally provided at both width direction ends of a web is welded to a base plate. The base plate is also fixed to first anchor bolts and to second anchor bolts, with the first anchor bolts and the second anchor bolts disposed at the opposite side of the flanges to the web. The second anchor bolts are also disposed at the web width direction inside with respect to the first anchor bolts. Therefore, load bearing ability of a column seat can be efficiently exhibited, and the thickness dimension of the base plate can be reduced.