To restrict deformation of a closed cross sectional surface of a pillar for improving its strength.

For center pillar 11 in a box structure having a closed cross sectional surface 11a in which both side end parts of an inner pillar panel 12, an outer pillar panel 13, and a center pillar reinforcement 14 are joined together, a reinforcement 15 is provided in the closed cross sectional surface 11a. The reinforcement 15 is provided with an inner flange 15a connected to the inner pillar panel 12 by spot welding, a general surface 15b extended in the car width direction, and an outer flange 15c connected to the center pillar reinforcement 14 by an adhesive, and the general surface 15b is disposed at a center in a vehicle longitudinal direction of the closed cross sectional surface 11a to devide the closed cross sectional surface 11a into two parts.