To provide a construction machine capable of reducing the discharge amount of grease when discharging water which has infiltrated into a grease bath from the grease bath.

An inner race 5a of a swing bearing 5, a peripheral wall plate part 32 and a bottom plate part 31 form the grease bath 40 composed of an annular recess, and the grease bath 40 is filled with the grease to lubricate the engagement part of a ring gear and a pinion 24. The peripheral wall plate part 32 includes a discharge port 50 for discharging the water which has infiltrated into the grease bath 40. Within the range of the liquid surface height of the grease (the range from the lowest liquid surface height position 60L to the highest liquid surface height position 60H), the position of a position adjusting member 52 is adjusted corresponding to the liquid surface height of the grease, that is the opening area of a discharge hole 51 is adjusted, and thus the discharge port 50 is provided on a position higher than the height position of the liquid surface of the grease.