Several low-friction-coefficient road-surface determination devices determine whether a road surface has a low friction coefficient based on the highest and lowest wheel speeds; the wheel speeds of front and rear wheels; wheel speeds of a left-hand and right-hand driving wheels; and by comparing a reference vehicle-body acceleration calculated from a driving force of an engine with an actual vehicle-body acceleration calculated from a calculated number of revolutions of differential gears. A low-friction-coefficient road-surface total-determination device makes a total determination as to whether the road surface has a low friction coefficient based on the determination results of the low-friction-coefficient road-surface determination devices. Accordingly, each low-friction-coefficient road-surface determination device is capable of compensating for disadvantages of the other devices.