Disclosed is an apparatus for preventing the drop of a work equipment of construction machinery for adjusting a descending speed of the work equipment when leakage occurs in a return line while the work equipment is descending. Provided is an apparatus for preventing the drop of the work equipment of construction machinery according to the present invention, comprising a hydraulic cylinder which is driven by hydraulic oil of a hydraulic pump; a control valve which is installed in a flow path between the hydraulic pump and the hydraulic cylinder; an operating lever; a drop prevention valve which is installed in a flow path between the control valve and the large chamber of the hydraulic cylinder; a return pressure first detection sensor which is installed in a flow path between the control valve and the drop prevention valve; and a controller for adjusting an opening area of the drop prevention valve when leakage occurs in the return line which returns the hydraulic oil from the hydraulic cylinder by a d
