A body structure for a railway car comprising: an outside sheathing of a side construction; a plurality of first reinforcement members arranged in a longitudinal direction of the railway car and being shaped like a hat in section, each of the first reinforcement members including a U-shaped part substantially U-shaped in section having a head part apart from said outside sheathing and two fitting flange parts extending continuously from end edges of said U-shaped part in opposite directions, said body structure being characterized in that said two fitting flange parts are joined to said outside sheathing by laser welding, and being further characterized by comprising: an opening portion (S1; S2) provided in said outside sheathing; and an inside plate frame (314C; 314D) including a body part extending substantially in parallel with said outside sheathing, first and second leg parts (314d, 314f; 314k) extending from the body part in a direction substantially perpendicular to said outside sheathing, a first flange part extending from the first leg part substantially in parallel with said outside sheathing and joined to said outside sheathing, and a second flange part extending from the second leg part substantially in parallel with said outside sheathing and joined to the head part of said first reinforcement member; wherein said inside plate frame is joined to free edge ends of said first reinforcement members outwardly of said free edge ends which extend toward said opening portion; and wherein said body part of said inside plate frame (314C; 314D) is joined to said U-shaped parts of said first reinforcement members, and said leg part extends continuously from said body part in such a direction as to close said free edge ends and covers said free edge ends, the free edge ends being located at said opening portion side. an outside sheathing of a side construction; a plurality of first reinforcement members arranged in a longitudinal direction of the railway car and being shaped like a hat in section, each of the first reinforcement members including a U-shaped part substantially U-shaped in section having a head part apart from said outside sheathing and two fitting flange parts extending continuously from end edges of said U-shaped part in opposite directions, said body structure being characterized in that said two fitting flange parts are joined to said outside sheathing by laser welding, and being further characterized by comprising: an opening portion (S1; S2) provided in said outside sheathing; and an inside plate frame (314C; 314D) including a body part extending substantially in parallel with said outside sheathing, first and second leg parts (314d, 314f; 314k) extending from the body part in a direction substantially perpendicular to said outside sheathing, a first flange part extending from the first leg part substantially in parallel with said outside sheathing and joined to said outside sheathing, and a second flange part extending from the second leg part substantially in parallel with said outside sheathing and joined to the head part of said first reinforcement member; wherein said inside plate frame is joined to free edge ends of said first reinforcement members outwardly of said free edge ends which extend toward said opening portion; and wherein said body part of said inside plate frame (314C; 314D) is joined to said U-shaped parts of said first reinforcement members, and said leg part extends continuously from said body part in such a direction as to close said free edge ends and covers said free edge ends, the free edge ends being located at said opening portion side. an opening portion (S1; S2) provided in said outside sheathing; and an inside plate frame (314C; 314D) including a body part extending substantially in parallel with said outside sheathing, first and second leg parts (314d, 314f; 314k) extending from the body part in a direction substantially perpendicular to said outside sheathing, a first flange part extending from the first leg part substantially in parallel with said outside sheathing and joined to said outside sheathing, and a second flange part extending from the second leg part substantially in parallel with said outside sheathing and joined to the head part of said first reinforcement member; wherein said inside plate frame is joined to free edge ends of said first reinforcement members outwardly of said free edge ends which extend toward said opening portion; and wherein said body part of said inside plate frame (314C; 314D) is joined to said U-shaped parts of said first reinforcement members, and said leg part extends continuously from said body part in such a direction as to close said free edge ends and covers said free edge ends, the free edge ends being located at said opening portion side.