A shutter structure includes a rotary shaft, a shutter plate, an upper rib and at least one lower rib. The rotary shaft is provided in a cylindrical duct line. The shutter plate rotates about the rotary shaft and switches between an open state and a closed state. The shutter plate has a peripheral edge portion, a curved portion, and a shutter plate shaft portion. The peripheral edge portion includes an upper shielding plate and two lower shielding plates. The lower shielding plates are located symmetrically to each other with respect to a center line. The center line is perpendicular to the shutter plate shaft portion. When the shutter plate is in the closed state, the upper shielding plate comes into contact with the upper rib from an upstream side, and the lower shielding plates come into contact with the at least one lower rib from a downstream side.