To provide a combining structure of the upper part of a center piece which can disperse the stress by the loading from the side surface.

A roof reinforcement 21 is formed in a closed section structure consisting of an upper 22 and a lower 23, and flanges 24 and 25 are formed at the ends respectively. A center pillar 11 is formed in a closed section structure consisting of a center pillar reinforcement 14 and a center pillar inner 13, and a connection 18 formed to the center pillar reinforcement 14 by a cutting out process is extended from an opening 20 formed to the center pillar inner 13 by a cutting out process, and it is jointed to a holder 19. And the flange 24 of the upper 22 is jointed to the joints at the front ends of the center pillar inner 13 and the center pillar reinforcement 14, and the flange 25 of the lower 23 is connected with the connection 18, so as to form an opened section structure, and a section structure continued from the center pillar 11 to the roof reinforcement 21 is formed.