A frame body (1) has a closed cross-section formed by a first surface (11), a second surface (12) wider than the first surface (11), and two side surfaces (13), and each of the side surfaces (13) has a single bent part (14) or two or more bent parts (14). In the cross-section of the frame body (1), the first surface (11) and an outer part (13a) of the side surface (13) form an angle of approximately 90 degrees or larger than 90 degrees inside the closed cross-section, and a specific bent part which is the single bent part (14) or one of the bent parts (14) closest to the second surface (12) is bent to protrude inward of the closed cross-section.