Abstract: A hydraulic disk brake apparatus especially useful for braking the rotation of a hoisting drum used to support a drill string in a well. The apparatus comprises a hydraulic fluid pump having an actuating lever, a pair of brake calipers having hydraulically actuated friction pads for engaging a brake disk coupled to the drum for rotation therewith, hydraulic fluid lines interconnecting the pump and the friction pads, and a mechanism for converting the braking reaction force caused by the torque applied to the calipers, when the pads engage the rotating disk, to an additional hydraulic force proportional to the amount of torque so applied to the calipers and applying this additional hydraulic force to the pads. This renders the braking action self-energized and provides a physical indication, i.e., a "feel", in the brake actuating lever reflecting the braking action actually take place on the drum.