To reduce the number of part items, simplify the structure, and reduce the rate of occurrence of failure to improve the reliability and reduce the cost by connecting a plurality of slats so as to be vertically adjacent to each other to constitute a slat group, and forming a number of small holes through the slabs.

A plurality of slats 16, 16... are connected so as to be vertically adjacent to each other to constitute a slat group 11, and its upper end part is mounted on a winding shaft so as to be capable of being wound/unwound. A number of small holes are formed through each of the slats 16, 16.... The diameter of the small holes is set to 1 mm or less, desirably about 0.8 mm so as to prevent the penetration of mosquitoes and insects. As the forming pattern of the small holes, a zigzag pattern having a pitch set to 1.6 mm is desired. Thus, the ventilation in use can be ensured, and protection of privacy and prevention of crimes can be attained.