PURPOSE: To join a steel frame to a beam through a pillar joint without cutting the pillar at every joint part and without connecting a pillar through diaphragm by forming the assembled section of a steel frame construction pillar into a construction in which square steel are fitted to the external angles of a square steel pipe.

CONSTITUTION: A shaped steel 2 is formed by a method in which shaped steel divided into four pieces are formed by hot extrusion of steel material and the plate parts of the two are welded to each other so as to form a divided half steel pipe, or a method of forming the divided half steel pipe by rolling, or a method of welding square steel to the bent angle of channel steel. After a diaphragm 1 is fitted to the shaped steel 2, 2 of which the external angles are fitted with square steel, they are welded so as to assemble a deformed square steel pipe in one body with square steel at the four corners. Hereby, the steel frame can be joined with a beam through a pillar joint.