Abstract: A shock absorber capable of exhibiting increased shock absorbing characteristics and constantly ensuring desired characteristics irrespective of applications intended. A cylinder is formed therein with a first hollow section of a large diameter and a second hollow section of a small diameter. A piston includes an end wall and a peripheral wall and is formed into a size sufficient to be moved in the second hollow section. The peripheral wall is formed with a plurality of orifices and the end wall is formed with a piston rod insertion through-hole and at least one viscous fluid passage hole. The piston rod is provided thereon with first and second flanges, which are spaced from each other at an interval larger than a thickness of the end wall of the piston and arranged so as to interpose the end wall therebetween.