PURPOSE: To increase the joint strength by mutually fitting the first and second ribs and the first and second grooves and attaching a flange part on a supporting surface, thus suppressing the turn-down of one car body skeleton part for attaching the edge part on the other car body skeleton part.

CONSTITUTION: The first rib 15 is installed on one 10 between the edge part of the outside of one car body skeleton part (center pillar) 10 and the outer edge part of the other car body skeleton part (side shill) 20, and the first groove 26 which is engaged with the rib 15 is formed on the other 20, and a supporting surface 22a directed inside the lateral direction is installed on the inside of the other car body skeleton part 20, and a flange part 13a in contact with the supporting surface 22a is installed on the inside in the lateral direction of one car body skeleton part 10. The second rib 14 in installed on one between the supporting surface and the flange part, and the second groove 24 fitted with the rib 14 is formed on the other. When the first and second car body skeleton parts are joined, the first and second ribs and the first and second grooves are fitted, and the flange part is attached on the supporting surface, and the joint strength of the first car body skeleton part for the second car body skeleton part is improved.