Apparatus and method for assessing condition of road surface

An apparatus for assessing the condition of a road surface comprising rotational speed detecting means for periodically detecting rotational speeds of four tyres of a vehicle; first computing means for computing slip ratio from measurement values of the rotational speed detecting means; second computing means for obtaining a relational formula between the slip ratio and acceleration/deceleration of the vehicle; and friction coefficient judging means for judging a coefficient of friction occurring between a road and a tyre on the basis of a slope of the relational formula obtained by the second computing means. The road friction coefficient mu can be judged with high accuracy in a short time by using only the wheel rotational speed information of four wheels. Thus, the performance and safety of a vehicle can be increased.