A damper unit includes: a cylinder, connected to a reservoir; a piston dividing an interior of the cylinder into two chambers; a piston rod which is connected to the piston at one end; an inner sleeve adapted to be accommodated within a hollow recess portion in the piston rod; a pump rod; a pump unit which performs pumping for generating a force with which the piston is pushed out of the cylinder or the piston is drawn into the cylinder; a hydraulic fluid releasing unit configured to release the a hydraulic fluid within the inner sleeve and the pump rod to the reservoir or the two chambers when the piston reaches a predetermined position relative to the cylinder within a sliding range thereof by pumping of the pump unit; and a control unit configured to control the predetermined position where the hydraulic fluid is released.