To provide a damper for reducing a damping force when the damper is elongated at a high speed without changing the damping force when the damper is shrunk.

A communication path 4a communicating a first liquid chamber 20 and a second liquid chamber 21 formed on a cylinder 2 is formed to a rod 4, and a shutoff valve 41 closing the communication path 4a is provided. The shutoff valve 41 opens the communication path 4a when a piston 3 slides at a speed exceeding a predetermined speed in a direction of the first liquid chamber 20, so as to reduce resistance of viscous fluid 6 against actions of the piston 3 and the rod 4.