A side construction 302 has an outside sheathing 306 and outside sheathing reinforcement members 307A and 307B joined to the outside sheathing 306 interiorly of the outside sheathing 306. The reinforcement member 307A (307B) is shaped like a hat in section. The reinforcement members 307A provided in the vicinity of a window opening portion have a laser welding spacing L1 of 80 mm and each have a hat width of 50 mm, while the reinforcement members 307B provided on other part have a laser welding spacing L1 of 100 mm and each have a hat width of 70 mm. The reinforcement members 307A and 307B each have a height of 25 mm.