To provide a road surface friction coefficient estimating device that can predict, in advance, a change in the coefficient of friction of a road surface to be run by one's own vehicle by obtaining information on a road surface friction coefficient at the position of the preceding vehicle without using inter-vehicle communication and the like, along with information on a road surface friction coefficient at the position of one's own vehicle.

The road surface friction coefficient estimating device comprises a wheel speed sensor 1 for detecting one's own vehicle speed, an inter-vehicle distance sensor 2 for detecting an inter-vehicle distance between the preceding vehicle and one's own vehicle, a one's own-vehicle-position road surface friction coefficient sensor 3 for detecting a road surface friction coefficient at one's own vehicle position, a relative speed computer 4 for differentiating the inter-vehicle distance from the inter-vehicle distance sensor 2 to compute the relative speed between the preceding vehicle and one's own vehicle, a preceding vehicle speed computer 5 for adding the related vehicle speed from the wheel speed sensor 1 and the relative speed from the relative speed computer 4 to compute the speed of the preceding vehicle, and a preceding-vehicle-position road surface friction coefficient computer 6 for estimating, through computation, a higher road surface friction coefficient at the preceding vehicle position as the absolute value of preceding-vehicle longitudinal acceleration as the derivative of the preceding vehicle speed is larger.