A road surface friction coefficient estimating device includes a lateral force detecting section for detecting the lateral force of a wheel during traveling, a slip angle detecting section for detecting the slip angle of the wheel during traveling, and a road surface μ calculating section for estimating the relationship between the detected lateral force and the detected slip angle on the basis of the ratio between the detected lateral force and the detected slip angle, the correlation between the lateral force and the slip angle in the case of the reference road surface, and at least either the detected lateral force or the detected slip angle.