A space frame comprises an upper frame body and a lower frame body both constructed with square steel tubular members; and diagonal members joining the upper frame body to the lower frame body. Each pair of two perpendicular sides of each of the square steel tubular members forming the lower frame body are arranged to make an angle of about 45 degrees to the plane of the lower frame body. The diagonal members are arranged to cross at an angle of about 45 degrees to bar members both of the upper and lower frame bodies. The space frame provides increased buckling strength because the bar members and the diagonal members may be entirely joined by welding.