A vehicle slip state determination
system serves to calculate an estimated vehicle speed VB, an estimated vehicle deceleration in the vehicle speed DVB, and each of wheel speed differences between right front and rear wheels and between left front and rear wheels ΔVR, ΔVL, respectively. The wheel speed difference ΔVR, ΔVL are divided into three ranges, that is, range 1, range 2, and range 3 by the speed difference upper and
lower limit values JVUP and JVLO, each of which is a linear function value with respect to the estimated vehicle deceleration DVB. In the ranges 1 and 3, the vehicle traveling on the road with the
low friction coefficient μ is brought into the slip state where four wheels are slipped. If the wheel speed difference at a predetermined estimated vehicle deceleration deviates from a determination range defined by the upper and
lower limit values, the slip state of the vehicle, that is, the condition where the vehicle is traveling on the road with the
low friction coefficient μ is determined.