To provide a draining structure for a flat sill of a sash, which is simple in structure and excellent in drain performance.

The sash is formed of a frame body consisting of a head, the sill, and right and left jambs, and shojis mounted in the frame body in a freely traveling manner, and the sill of the sash has an almost flat upper surface. The sill 10 has recessed slots 13, 13 on indoor and outdoor sides thereof, in which lower beds of bottom rails of the inside and outside shojis are arranged, respectively. Then, a hollow portion 103 is formed below the recessed slots 13, 13, and a drip hole 100 for guiding water infiltrating into a portion of each recessed slot 13, closed by the shoji, into the hollow portion 103 is formed in a lower surface of each recessed slot 13. Further, a first drain hole 101 for draining water guided from the drip holes 100 to the hollow portion 103, to the outside is formed in an outside sidewall surface of the hollow portion 103, and a second drain hole 102 for directly draining water entering an outward exposed portion of the outside recessed slot 13, to the outside is formed in an outside sidewall surface of the recessed slot 13.