A one-way damper has a rotor which is provided with a braking disc at one of its ends. The braking disc is received in a housing of the damper and the housing is filled with oil. The other end of the rotor extends outward from the housing and has a gear loosely mounted thereon. The gear is engaged with a coil spring. When the gear rotates in one direction, the coil spring is reduced in diameter so that it grips the rotor, making it possible for the torque of the gear to be transmitted to the rotor through the coil spring. When the gear rotates in the other direction, the coil spring is expanded in diameter so that it does not grip the rotor, making it possible for the gear to turn freely. The one-way damper is used in association with a lid or door to damp one but not the other of the opening and closing operations.