PURPOSE: To simplify wiring of a wire tension mechanism and to improve appearance.

CONSTITUTION: A fitting wire screen device main body 10 comprising movable members 13, 14 and pleated net members 15, 16 which can be freely folded and expanded to open and close, following the movement in the opening and closing direction X of the movable members is fitted between both upper and lower frames 2, 3 of a wire screen fitted frame part 7 provided on a sash frame 1 where an opening part such as a window part of a building or the like is formed. The movable members 13, 14 of the fitting wire screen device main body are stretched in such a manner as to be self-supported for preventing oscillation in the moving direction by a wire tension mechanism 20 comprising first and second upper and lower wires 21, 22. Both upper and lower wires 21c, 22c extended from both upper and lower end parts 13a, 13b and 14a, 14b of the movable member and laid in the intersecting state in the inside to be extended to the outside are provided in such a manner as to be guided along storing shading parts 30, 40 formed on both upper and lower frames of the wire screen fitted frame part.