PURPOSE: To promote the facilitation of manufacturing work of a car body structure by making improvements in strength per unit and also reducing the number of part items.

CONSTITUTION: A side pole 2 installed in the circumference of a window of a vehicle and set up in the vertical direction is integrally formed so as to have a reinforced part 5 with the same circular radius R as a circular radius R in a window corner part of an outer plate 4 situated in a joint part of a belt rail 3 set up in the horizontal direction. With this constitution, stress concentration in the window corner part is reducible, while any possible occurrence of a strain is abated, and thereby the manufacture of a car body is made easy in addition to being lighter in weight.