To perform the automatic welding of a transverse girder capable of preventing occurrence of the welding distortion in the welding and assembly process of panels at a construction site.

A panel structure comprises a metal plate 2, longitudinal members 3 which are welded on the metal plate 2 with the prescribed intervals, and transverse members 4 which are welded at the position where transverse girders 5 are arranged when the members are joined with each other, and the transverse members are welded on the metal plate at the same height as the longitudinal members away from the longitudinal members, and reinforcement members 6(7) is welded to at least either one side edge of the metal plates in the panel structure in the direction parallel to the longitudinal members or one side edge in the direction orthogonal to the longitudinal members. A plurality of panel structures are arranged so that the longitudinal members 3 and the transverse members 4 are on the line respectively, and the metal plates 2, the longitudinal members 3, and the transverse members 4 of the adjacent panel structures are welded to each other to constitute a panel structure connection body on which the transverse girder 5 is welded on the transverse members.