PURPOSE: To provide a buffer capable of smoothly stopping a moving body such as a work as well as minimizing time required for buffing the moving body in accordance with strength of kinetic energy of the moving body.

CONSTITUTION: In a hole 1b provided on a rear part wall of an outer case 1, a male screw member 3 is supported by an operation shaft 2 free to revolve. On a rear end recessed part of a dmaper case 5, a female screw part 5a is formed. Inside of the damper case 5, an orifice groove 5e the flow passage sectional area of which gradually decreases from the front toward the rear is formed. When the male screw member 3 is turned, the damper case 5 advances or retreats, and a position of the orifice groove 5e against a stroke range of a piston 11 is changed. Consequently, as strength of reaction generated all over the stroke range of the piston 11 is changed, strength of energy which can be absorbed is changed.