Closing device for a gas-conducting line, the closing device having a first connection side with a first opening and a second connection side with a second opening, the closing device further having a plurality of closing elements with a substantially flat extension, which are arranged in and can be pivoted in a working plane, so that the closing elements block a flow of gas in a closed position and allow a free flow of gas in a flow position, wherein each closing member has a first bounding side of its substantially flat extent and a second bounding side of its substantially flat extent, which are formed complementary to each other, so that each closing element bears positively against the adjacent closing elements in the closed position, so that the substantially flat extensions block the flow, and wherein the adjusting element can be actuated from outside the base body.