In an anti-lock control arrangement for preventing locking of vehicle wheels, a prescribed speed difference of a threshold speed from an estimated vehicle speed is changed from an initial value of the difference to a larger value when a wheel speed has been lower for a prescribed time than the threshold speed which follows the estimated vehicle speed with the prescribed speed difference therefrom or when a prescribed statement with respect to the wheel speed is repeated at a predetermined number. Further, the speed difference of the threshold speed from the estimated vehicle speed is changed back to the initial value when the wheel speed has become lower than the threshold speed subjected to the former change.