Device for estimating road friction state

A device for estimating a road friction state in which a friction state of a wheel with respect to a road surface can be estimated accurately. A bandpass filter extracts, from a wheel speed signal detected by a wheel speed detecting unit, a portion of the wheel speed signal in a predetermined range which includes a torsion resonance point at which a frequency is greater than a low frequency regions. A vibration level computing unit computes a vibration level of the wheel speed signal. A road friction state estimating unit estimates the friction state of the wheel with respect to the road surface on the basis of a vibration level computed by the vibration level computing unit and an estimated value of a road mu slope computed by a mu slope computing unit, and on the basis of a relationship between the two determined for each road surface state.