To provide a barrier-free type structure of an outdoor sash with a flat sash, which is mounted in the entrance of an building opening for separating indoor and outdoor spaces from each other, in which a top surface of the sill of the sash is almost flatly formed with no rail groove, which is excellent in drainability of rainwater etc. attended with wind pressure, and which has high watertightness against indoor water leakage.

A sealing means is provided between the sash and the sill so that a sealing part can be pressed when the wind pressure is imposed on the sash from the outdoor side; a drainage groove is provided on the tops surface of the flat sill; a water collecting recess wider than the drainage groove is provided immediately underneath the drainage groove; a recess drain inlet is provided in the bottom of the water collecting recess; a guiding hollow part for guiding the rainwater outdoors is provided directly below the recess drain inlet; an outdoor drain inlet is provided on the outdoor side of the guiding hollow part; and the water collecting recess and the guiding hollow part communicate with outside air.