DOUBLE WINDOW, INNER WINDOW OF DOUBLE WINDOW, AND METHOD OF FORMING DOUBLE WINDOW

PROBLEM TO BE SOLVED: To provide a double window which can improve thermal insulation performance while performing ventilation.SOLUTION: A double window includes: an outer window 1 which is provided with an outer sash 12a and an inner sash 12b openable and closable to a frame 11 in a double-sliding manner; and an inner window 2 which is provided with an outer sash 25a and an inner sash 25b openable and closable inside a frame 24 in a double-sliding manner; a ventilation part 4 which forms a number of vent holes in a top rail 16 of the outer window 1 to communicate with the inside and outside of a room; and a ventilation part 5 which forms a number of vent holes 32b in an upper frame 26 of the inner window 2 to communicate with the inside and outside of the room. A resistance part 6 which gives a resistance to an air flow is installed in one of the ventilation parts 4, 5. Air flows between the inside and outside of the room through the ventilation part 4 of the outer window 1, an intermediate layer 3 between the outer window 1 and the inner window 2, and the ventilation part 5 of the inner window 2.