PURPOSE: To improve work efficiency by temporarily fixing positioning nuts to anchor bolts on a foundation for fixing of a column base in positions corresponding to the upper surface of base mortar that is covered with a soft sheet made of synthetic resin, and by pressing a form board that is fitted to the bolts down to the position of the nuts.

CONSTITUTION: To anchor bolts 2 that are planted to a foundation 1 for fixing of column base of a steel column, positioning nuts 3 are respectively screwed down and are temporarily fixed, after making adjustment by screwing, to positions corresponding to the upper surface of a base mortar 4. The base mortar 4 is heaped up on the foundation 1 and is covered with a soft flexible seat 5 made of synthetic resin. Through holes 6a are bored to a form board 6 and are penetrated with the anchor bolts 2. The board is then made to touch the base mortar 4 and is further pressed down for touching with the nuts 3. Thereby the upper surface of the base mortar can be levelled exactly to a specified level.