A lubricant draining device for draining a lubricant from a closed mechanical section (20) provided in a machine structure such as a robot, a machine tool and an injection molding machine. The lubricant draining device includes a wall (24) defining the mechanical section, the wall including a drain port (26) communicated with an interior space of the mechanical section while permitting a lubricant to flow therethrough; a tube (28) connected at a proximal end (42) thereof to the drain port and permitting a lubricant to flow therethrough; a blocking member (30) blocking a flow of lubricant through the tube in a releasable manner; and a retaining section (32) retaining the tube at a location adjacent to the wall with the tube being kept connecting with the drain port. The retaining section may include a chamber (46), provided on the wall (24), for accommodating the tube (28) in its entirety with the tube being removable from the chamber. The chamber may be provided with a detachable cover (50).