To shield a gap in the lower side of a sliding screen in the case the ventilator is closed and to ensure water tightness in the lower side of the sliding screen in a state to close the sliding screen, if necessary.

A sash is equipped with a door frame having a sill approximately flush with the floor surface, a door 1 and a tight material 13 provided to the bottom rail 1A in a vertically movable manner. It is equipped with a tight material operating mechanism 10 with the closing and opening of the door 1 and a tight material pushing mechanism 30 press-contacting the tight material 13 coming into contact with the sill in advance in a door closing state.