Bodyshell structure of railcar

1. A bodyshell structure of a railcar, comprising:

a side bodyshell including an outside plate portion, an inside plate portion, and a joint portion configured to join the outside plate portion and the inside plate portion;

an inside window opening formed on the inside plate portion and provided inside the railcar; and

an outside window opening formed on the outside plate portion and having a smaller opening area than the inside window opening, wherein:

the outside window opening has an oval shape extending in a railcar longitudinal direction or a circular shape;

the side bodyshell is formed by joining at least an upper side bodyshell and a lower side bodyshell, which are separable in a railcar vertical direction;

a joint portion of the upper side bodyshell and the lower side bodyshell is located at a straight portion formed at the outside window opening and the inside window a opening to extend in the railcar vertical direction; and

a length of the straight portion is 1% to 10% of a vertical height of the inside window opening.

2. The bodyshell structure according to claim 1 , wherein the inside window opening is formed by cutting off the inside plate portion and the joint portion.

3. The bodyshell structure according to claim 1 , wherein each of a length of the inside window opening in the railcar longitudinal direction and a length of the outside window opening in the railcar longitudinal direction is larger than an interval between seats adjacent to each other in the railcar longitudinal direction.