A seat cushion frame structure of a seat for a vehicle has an oblique monolithic strip on at least one of a pair of side frames an upper end of which is fixed to a side portion of the at least one of pair of side frames and a lower end of which is fixed to the seat cushion frame structure at a position forward of the upper end. The oblique monolithic strip is arranged in such a way that one of its strip surfaces opposed to each other is oriented to be upward, its cross section perpendicular to the opposed strip surfaces is a rectangle long in a lateral direction and includes at each of its upper and lower ends a wound portion which is wound in a loop manner in such a way that the one of said opposed strip surfaces is oriented to be inward.