A center pillar includes a first reinforcement panel which is arranged between an outer panel and an inner panel, comprises a bottom wall portion, both-side vertical wall portions extending in a vehicle width direction from the bottom wall portion, and both-side flange portions, and has a cross section formed in substantially a hat shape. A second reinforcement panel comprising a bottom wall portion and both-side vertical wall portions and having a cross section formed in substantially a U shape is arranged inside the first reinforcement panel. The second reinforcement panel is joined to the first reinforcement panel such that only the bottom wall portion and one of the both-side vertical wall portions are joined to the bottom wall portion and one of the both-side vertical wall portions, respectively.