A reinforcing structure of a vehicle frame member includes: ribs that integrally connect standing wall portions, that are formed at a planar portion of a vehicle frame member, to one another, and that reinforce the planar portion; portions of gradually changing thickness that are formed at connected portions of the ribs with the standing wall portions; portions of gradually changing height that are formed at the connected portions of the ribs with the standing wall portions; first curved portions that are formed at the portions of gradually changing thickness; second curved portions that are formed at the portions of gradually changing thickness; third curved portions that are formed at the portions of gradually changing height; and fourth curved portions that are formed at the portions of gradually changing height.