To prevent small foreign matter swirling in the vicinity of the central part of a swirl chamber from flowing into the inside of a partition member.

A swirl vane 11 is arranged at an annular space 10 formed by an upper casing 3 and an exhaust pipe 5. The upper part of the annular space 10 is connected to an inlet 7 and its upper part is connected to an outlet 12 through an inside hole of the exhaust pipe 5. A swirl chamber 14 is formed below the annular space 10 and a drain valve chamber 15 is formed below the swirl chamber 14. A valve float 19 is arranged in the drain valve chamber 15, and a reverse cup-shaped partition member 20 is arranged between the swirl chamber 14 and the drain valve chamber 15. A ventilation hole 23 communicating inside and the outside is formed at an upper part of the partition member 20, and a liquid passage hole 24 communicating the inside and the outside is formed at a lower part. A partition cylinder 25 partitioning the drain valve chamber 15 inside and outside, closing a lower end, and opening an upper end above the liquid passage hole 24 of the partition member 20 is provided outside the outer circumferential wall of the partition member 20. The upper end opening of the partition cylinder 25 is covered with a filter 29 having many filtering holes for capturing small foreign matter.