A flat spring (10) for a railroad vehicle bogie according to the present invention comprises an upper surface member (12) formed from a fiber-reinforced plastic in which the reinforcing fibers are laminated so as to extend in the longitudinal direction, a lower surface member (14) formed from a fiber-reinforced plastic in which the reinforcing fibers are laminated so as to extend in the longitudinal direction, and a core member (16) disposed between the upper surface member (12) and the lower surface member (14). The core member (16) is configured from a fiber-reinforced plastic in which the reinforcing fibers are laminated in the widthwise direction, which is the direction orthogonal to the lamination direction in the upper surface member (12) and the lower surface member (14), in a manner such that the reinforcing fibers are inclined with respect to the bending neutral axis and intersect each other when viewed from the side of the core member (16).
