To prevent the deformation of a rear frame bent part due to a shock from the rear and suppress cross sectional deformation of a rear frame due to a shock from a side.

In this rear frame structure provided with the rear frame 1 extending in the forward and backward directions of a vehicle body along both side parts of the vehicle body, having a bent part 1a bending at least upward from the front to the rear in the vicinity of a fuel tank 8, and having a closed cross sectional shape and cross members 3, 4 connecting right and left rear frames 1, a reinforcement 7 having a main vertical wall part 71 positioned along substantially forward and backward directions of the vehicle body in a cross section of the bent part 1a and an auxiliary vertical wall part 73 continuous with at least either of a front side and a rear side of the main vertical wall part and positioned along substantially direction of vehicle body width is provided therein. The auxiliary vertical wall part 73 of the reinforcement 7 is arranged along substantially an extension line of a vertical wall part 41 of the cross member 4.