A shock absorber with a possible minimum peak value of the impact acceleration during a collision. The shock absorber includes a tubular cylinder part with an opening at one end and the other end closed, a seal part configured to seal the internal space of this cylinder part at a part closer to this one end inside this cylinder part, fluid filled in the enclosed space formed by this seal part inside this cylinder part, a slidable piston part inside this enclosed space, and a rod part that slidably penetrates this seal part concentrically and is connected to this piston part at one end while projecting out to the other side. This cylinder part has a tapered inner surface inside this enclosed space, reducing its internal diameter from the one end to the other end, and the rate of this taper is within the range from 1/50 to 1/130.