The present invention provides a draining device for a construction machine enabling to easily and safely perform draining work of a cooling system. A drain cock 33 of a radiator 27 radiating heat ofcooling water cooling an engine 20 is provided on a surface facing a side surface cover 19c provided on a side surface of an engine compartment 19 in such a manner that the same can freely open and close, and another end of a drain pipe 35 of which one end is connected to the drain cock 33 is extended out of the engine compartment 19 from a small hole 34a formed on an under cover 34 covering a bottom surface of the engine compartment 19. Draining work of a cooling system can be performed easily and safely, and also since it is enough to form just the small hole 34a for extending out the drainpipe 35 on the under cover 34, blowing sound of a cooling fan 24 and engine sound don't leak to an outside and don't cause noise problem and strength of the under cover 34 is not dropped.