To provide grid-pattern frameworks easy to assemble and low in manufacturing cost and double layer grid-pattern frameworks using them.

A grid-pattern framework easy to assemble and low in manufacturing cost is provided by forming a ligulate piece 3 by fitting a steel plate in a slit 2 of an end part of a square steel pipe 1 and welding it, mating the square steel pipes 1 having these ligulate pieces 3 with each other in a grid- pattern, putting connecting plates 4, 5 on each of the ligulate pieces 3 of this mated grid point from both of upper and lower sides and connecting each of the ligulate pieces 3 and these connecting plates 4, 5 by bolts 6. Additionally, a plural number of layers of the grid-pattern frameworks constituted by forming upward or downward installation parts on the connecting plates 4, 5, arranging the grid-pattern framework with the downward installation part formed on it on the upper side and the grid-pattern framework with the upward installation part formed on it on the lower side and to connect connecting members on these installation parts in a truss shape are provided.