PURPOSE: To promote quietness efficiency in the case of opening and closing of a shutter by forming projected and recessed coupling sections of corner sections and flat sections in both upper and lower edges by bending, contacting subsequently the mutual corner sections and flat sections of coupling sections alternately in the case of turning, and bringing into contact with the flat sections though the corner sections.

CONSTITUTION: A projected coupling section 4b consisting of corner sections F-J and flat sections(f)-(j) is formed in an upper edge of a shutter curtain slat 4 by bending, and a recessed coupling section 4a consisting of corner sections A-E and flat sections (a)-(e) is formed in a lower edge by bending. Bending angles H and E of the corner sections involved in an overlapping state are formed so that they are smaller than bending angles D and I of the corner sections involved in. When a shutter is rolled up and down, the corner sections and the flat sections are subsequently contacted alternately with each other, and the flat sections are contacted through the corner sections. According to the constitution, sounds caused by slat contact can be reduced in the case of opening and shutting.