The estimating method for a road friction coefficient μ includes the steps of detecting a steering angle by a steering angle sensor; detecting a lateral acceleration by a lateral acceleration sensor; and calculating an approximate friction coefficient μ by referring to a road friction coefficient μ determination table where a plurality of regions each composed of steering angle and lateral acceleration are defined so as to respectively correspond to a plurality of road friction coefficients μi (i=1 to n, n is an integer not less than 2) on the basis of a boundary line derived from lower limits of the lateral acceleration over various values of the steering angle, and by specifying one of said regions according to the steering angle detected by said steering angle sensor and the lateral acceleration detected by said lateral acceleration sensor to thereby specify one of said road friction coefficients μi as said approximate friction coefficient μ.