To provide a drain circuit for turning motors for returning drain from plural turning motors to a hydraulic oil tank in which sludge or dust generated in one turning motor is not carried into the other turning motor.

A thickness and a length of each piping are set in such a way that pressure losses in drain circuits 10 and 12 from drain outlets 1a or 2a of two turning motors 1 and 2 to a confluence P are roughly equal to each other. Piping lengths of the drain circuits 10 and 12 are, favorably, roughly similar to each other. A height of the confluence P is, favorably, set to be lower than that the drain outlet la and 2a of the turning motors 1 and 2.