To prevent the air tightness of a free piston from becoming worse due to the separation of an inner face burr on an inner wall face in a junction part of a cylinder caused by frictional pressure contact junction.

The separation-fallen inner face burr 13 stays in a space 14 to be deterred from being advanced to a free piston side by positioning the inner face burr formed at the inner wall face 7b' of the junction part 7b between a cylinder body 8 and a cylinder cap 9 forming the cylinder 7 of a shock absorber 1 in the space formed of an inner wall face 7a of the cylinder 7, an inner wall face 9a and an inner bottom 11 of the cylinder cap 9, and an inverted truncated cone-shaped rib 12 of the inner bottom 11 of the cylinder cap 9, and the air tightness for the free piston and the inner wall face of the cylinder is secured without damaging those, and the attenuation of an input load is thereby maintained over a long period of time.