PURPOSE: To simplify the car body structure of an automobile by connecting the end part of a side member and the end part of a cross member to each other through a gusset having its closed cross section and bending the extended part of an outer member so as to be connected to two surfaces sandwiching the outside surface of the gusset and the corner part of a cross member end.

CONSTITUTION: The mounting flange 6C of a gusset 6 fixed on a cross member 5, is connected on the inner bottom wall 21 of an inner member 2, and a mounting flange 6B is connected on the lower surface of an opening side lower wall 22, and also a mounting flange 6A is connected on the flat plate outer wall part 30 of a first outer member 3, and a lower mounting flange 2B is held by a mounting flange 61A and the flat plate outer wall part 30. Therefore, in addition to connecting the cross member 5 and a side member 1 to each other by the gusset 6, the lower end bent part 32 of the first outer member 3 is put over the fixed surface 52 of the cross member 5 so that connecting rigidity between the cross member 5 and the side member 1 can be extremely improved.