In a seat cushion frame which comprises side frames fixed to each of the two ends of a pan frame in the width direction, the rigidity of mounting the side frames to the pan frame is increased. In this seat cushion frame having a configuration in which side frames are fixed to both ends of the pan frame in the width direction, the side frame is fixed to the pan frame with a flange formed by bending the top part inwards in the width direction, and a recess recessed inwards in the width direction is formed in the portion of the flange that is fixed to the pan frame.