therefrom corresponding to the both sides of the wheel rim 60 of the bicycle a pair of protrusions 31 are formed at a side of the sliding assembly 30 corresponding to that protrusions 27 of the brake shoe holder 20 the sliding assembly 30 also has a gradient face 32 slantingly formed outwardly in accordance with the direction of the rotation of the tire of the bicycle at the bottom thereof which is in corresponding to the gradient face 26 of the brake shoe holder 20 the spring 50 is accommodated in the recess 21 of the brake shoe holder 20 having a first end engaged with the protrusions 27 and a second end engaged with the protrusions 31 of the sliding assembly 30 referring further to the fig5 8 which shows the first embodiment of the present invention in the fig5 shows the status of the anti lock brake system of the present invention before a braking action being operated in which the brake shoe holders 20 at both ends of the mounting bracket 61 are apart from the wheel rim 60 of the bicycle by virtue of the mounting bracket 61 the sliding members 30 are pushed to one end of the recesses 21 of the brake shoe holders 20 by.