To adsorb dew condensate generated on sashes or panes in a cold time and evaporate it to the indoor side by filling silica gel in the hollow window frame base and forming introducing holes for the condensate and openings for emission of moisture.

A sash 1 is attached to a hollow window frame base whose both ends are closed by waterproof caps, through a heat insulation material 7, and the window frame base is filled with silica gel 2 and further, a water absorptive material 4 is filled in introducing holes for dew condensate hales 3 formed in the sash 1, and further, moisture emission openings 5 are formed through a mesh 6 in the indoor side. In this way, dew condensate generated on the indoor side of a sash 1 or a pane is forced to adsorb in the silica gal 2 through the water absorptive material 4 and also the vapour is emitted to the indoor side through the moisture emission openings 5. Meanwhile, the indoor air in contact with the sash 1 and the pane forms a downflow stream owing to cooling and accelerates evaporation. Accordingly, dew condensate generated on a window can be treated without use of a heater, a motor, etc.