To provide a steam trap capable of preventing an outlet passage from being eroded.

A valve chamber 6, at an upper part of which an inlet 3 is opened, and the outlet passage 5, which is arranged by being away from the valve chamber 6 and at an upper part of which an outlet 4 is opened, are formed at casings 1, 2. A valve seat member 12, in which a valve hole 10 is opened at a valve chamber 6 side end and a branch hole 11 is opened at an outlet passage 5 side end, is provided at a lower part of the outlet passage 5, the valve chamber 6 is communicated with the outlet passage 5 and a spherical float 15 as a valve member for opening/closing the valve hole 10 is arranged in the valve chamber 6. A guide rod 17 is fixed in the valve seat member 12 and a helical cutout 18 is provided at an outer surface of the guide rod 17. Condensed water flowing down in the valve hole 10 passes through the branch hole 11 while revolving by the helical cutout 18 of the guide rod 17 and then collides with an inner wall of the outlet passage 5. Since local collision of the condensed water at a part of the outlet passage 5 does not occur and the condensed water dispersively collides with the outlet passage 5, the outlet passage 5 is prevented from being eroded.