A damper device comprising: a frame in which an opening part is formed; a baffle configured to open and close the opening part ; a drive mechanism structured to drive the baffle ; and a case which accommodates the drive mechanism ; wherein the drive mechanism comprises a stepping motor and a gear train structured to transmit rotation of the stepping motor ; wherein the gear train comprises a drive gear and a sector gear engaged with the drive gear and driven by the drive gear ; wherein a first lock mechanism is structured between the drive gear and the sector gear at a movement restricted position in one of a closing direction and an open direction of the baffle , and the first lock mechanism prevents turning of the sector gear to the other of the closing direction and the open direction of the baffle ; and wherein the first lock mechanism is structured so that a first circular arc-shaped outer peripheral part of the drive gear concentrically formed so as to have the same or larger diameter than a tooth tip circle of a partially toothless gear engaged with the sector gear and disposed at a position adjacent in a circumferential direction to the partially toothless gear is entered into a portion of a tooth whose dimension in an axial line direction is narrowed of a plurality of teeth of the sector gear engaged with the drive gear and thereby the sector gear is restricted; the damper device being characterized in that a tooth on a most first circular arc-shaped outer peripheral part side of the partially toothless gear is formed so that a curvature of a first tooth face on an opposite side to a first circular arc-shaped outer peripheral part side is smaller than a curvature of a second tooth face (682c2) on the first circular arc-shaped outer peripheral part side. a frame in which an opening part is formed; a baffle configured to open and close the opening part ; a drive mechanism structured to drive the baffle ; and a case which accommodates the drive mechanism ; wherein the drive mechanism comprises a stepping motor and a gear train structured to transmit rotation of the stepping motor ; wherein the gear train comprises a drive gear and a sector gear engaged with the drive gear and driven by the drive gear ; wherein a first lock mechanism is structured between the drive gear and the sector gear at a movement restricted position in one of a closing direction and an open direction of the baffle , and the first lock mechanism prevents turning of the sector gear to the other of the closing direction and the open direction of the baffle ; and wherein the first lock mechanism is structured so that a first circular arc-shaped outer peripheral part of the drive gear concentrically formed so as to have the same or larger diameter than a tooth tip circle of a partially toothless gear engaged with the sector gear and disposed at a position adjacent in a circumferential direction to the partially toothless gear is entered into a portion of a tooth whose dimension in an axial line direction is narrowed of a plurality of teeth of the sector gear engaged with the drive gear and thereby the sector gear is restricted; the damper device being characterized in that a tooth on a most first circular arc-shaped outer peripheral part side of the partially toothless gear is formed so that a curvature of a first tooth face on an opposite side to a first circular arc-shaped outer peripheral part side is smaller than a curvature of a second tooth face (682c2) on the first circular arc-shaped outer peripheral part side. <EOS>