A damper includes a cylindrical housing; a rotor rotationally housed in the cylindrical housing; a biasing member for applying a biasing force to the rotor; viscous fluid filled in the cylindrical housing; and a spare winding setting device for setting the biasing force of the biasing member. When the rotor rotates, the rotation is damped by a shear resistance of the viscous fluid filled in the cylindrical housing. The damper may include an open position lock mechanism having a first engaging projection disposed on an inner circumferential surface of the cylindrical housing and a second engaging projection disposed on an outer circumferential surface of the rotor. The first and second engaging projections can engage or move over with each other.