Through holes 14, which passes through a side wall portion 12b of an outer reinforcement 12, is formed at a lower portion of a center pillar 1. The through hole 14 is formed substantially in a D shape, and includes a linear portion 14a and a circular are portion 14b that is connected to both ends of the linear portion 14a. The length of the circular arc portion 14b is longer than that of the linear portion 14a. The linear portion 14a is disposed close to the inside of a vehicle, and the circular arc portion 14b is disposed close to the outside of a vehicle. If the circular arc portion 14b allows for deformation in length as described above, tensile stress is not easily applied to the circular arc portion when a load F is applied to the center pillar by a side collision. Accordingly, the fracturing of a center pillar 1 does not easily occur.