PURPOSE: An auto brake unit of a cable drum is provided to control the danger of a cable drum rotating in overspeed by installing a break block supporting the rotation of the drum. CONSTITUTION: The automatic brake of a cable drum is comprised of a sensor(12), a brake block (K), a hydraulic motor(40), a hydraulic system, and a controller(51). The sensor measures the speed of a cable attached to the outside of a caterpillar(10). The brake block is arranged in the bottom of the cable drum which is formed in a circular plate(21) in both sides. The hydraulic motor is fixed to a screw bolt(30) in the end of the brake block through a coupler. The hydraulic system has a hydraulic line to rotate the hydraulic motor.
