PURPOSE: To permit the improvement of thermal environment at a low cost, by a method wherein a vertical frame is constituted in a sash at the inside of a window and the end of a louver, inserted into the duct, is provided with a required number of fins to permit heat exchange between hot air or cold air supplied to the duct.

CONSTITUTION: The inner vertical frame of a sash in a window 2 is constituted so as to be a duct 3 having a vertical guide groove 4 on the side surface thereof while louvers 7, 7,... of a blind 6, located at the inside of a window glass 5, are inserted into the guide groove 4 of the duct 3 so as to be capable of moving freely into up-and-down direction. Respective louvers 7, 7,... are formed of flat type heat pipes, which are connected mutually so that the angle thereof is controlled freely and are attached so that the shutter plates 9, 9,... of the guide groove 4 are positioned so as to be superposed with each other, while fins 8, 8,... are attached thereto from the shutter plate 9 to the end of the louver. A blind receiving box 10, provided above the upper horizontal frame 11 of the sash, is provided with a guide groove 12 for receiving louvers in the box and the blind 6 may be extracted out of the guide groove 12.