The invention provides a vehicle drive assistance system and a vehicle drive assistance method, which can maintain a driving performance of a vehicle driver through providing drive assistance. The vehicle drive assistance system (S) is provided with a required driving ability estimating unit (D estimating unit) (22) to estimate a required driving demand (D) (required driving ability) of a driver (E) for driving a vehicle (V) in a traffic environment based on a traffic environment around the vehicle and drive assistance provided to the driver (E) by the vehicle (V); a current driving ability estimating unit (P estimating unit) (21) to estimate a current driving performance (P) (current driving ability) of the driver (E); and a changing unit (23) to perform increase processing in which the driving demand (D) is increased when the driving performance (P) is higher than the driving demand (D).