A frame structure for a purpose built vehicle (PBV) includes: two main side members extending while gradually rising toward a front of the PBV and extending in a front/rear direction to be disposed on either side of the PBV; two auxiliary side members respectively extending in a front/rear direction to be disposed on a lower side of the two main side members; a front cross member connecting the two auxiliary side members in a lateral direction of the PBV; and a plurality of vertical members respectively connecting the main side members and the auxiliary side members in a vertical direction.