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.