Abstract: In a junction structure between structures formed by connecting a hollow rectangular beam having a rectangular cross section between a first column and a first? column, the beam has a first beam, a second beam, and a first? beam from the first column toward the first? column. Three surfaces other than an upper surface of the first beam and three surfaces other than an upper surface of the second beam are sandwiched between plates from inner and outer sides and joined together with bolts, and the upper surfaces are joined to each other by welding contact portions of an upper portion of the first beam and an upper portion of the second beam.