PURPOSE: To simplify tension adjustment and wiring work for a wire tension mechanism so as to improve work efficiency and reduce the cost.

CONSTITUTION: A fitting wire screen device main body 10 is of a center opening structure comprising first and second movable members 11, 12 and a net member 13 provided between the movable members 11, 12. The first and second movable members 11, 12 are self-supported by a first wire tension mechanism 40 and a second wire tension mechanism 50 which are independent from each other. The wires 41, 42, 51, 52 of the first and second wire tension mechanisms 40, 50 are stretched by fixing the wires to an upper guide rail 6 and a lower guide rail 7, respectively, which are fitted to both upper and lower frames 2, 3 of a sash frame 1.