Abstract: A method of forming a base structure assembly used in a wooden axial structure in wooden architectural construction includes the steps of forming a basic foundation, positioning a joint part having a supporting leg serving as an anchor bolt, fixing a each end of prepared base members, one after another, to base member joint portions which face each other, adjusting a level thereof, completing a base construction or a floor structure, and forming a basic concrete structure between the base foundation and the lower part of the base. Joint parts conducting the method includes pillar leg joint portions which is provided at the top end of a bar member wherein a pillar legs are inserted into, base member joint portions provided around said top end of said bar, a supporting leg provided at the lower part of said bar, and a level adjusting mechanism incorporated in the proper place of the bar.