A preform for a fiber-reinforced composite material including a bent portion along a curved line for bending, a flange portion corresponding to an outer circumferential portion, and a semi-cylindrical portion formed by bending an inner circumferential portion along the curved line for bending located in a flat plane or a curved plane region. The preform is formed from a precursor having a predetermined extension. The outer circumferential portion corresponds to a first region where a first plurality of reinforced fibers is partially disposed in parallel along the curved line for bending. The inner circumferential portion corresponds to a second region constituted solely of a second plurality of reinforced fibers disposed throughout the entire area, so as to intersect the first plurality of reinforced fibers at a predetermined angle in the first region.