PURPOSE: To prevent dispersion particles from infiltrating into a relative slide portion such as the one between the rod portion of a piston and the end cap of a cylinder.

CONSTITUTION: This shock absorber has a cylinder 10 and a piston 20 that is put into the cylinder 10 reciprocatably and delimits two chambers in cowork with the cylinder 10, and at the piston 20, a throttle passage 30 to connect two chambers to each other, and a pair of electrodes 32, 34 that form an electric field across the throttle passage 30, are provided. In the cylinder 10, a diaphragm 42 is provided between the rod portion of the piston and the cylinder 10, and the intrusion of the dispersion particle of an electroviscous fluid 56 into a fitting portion between the rod portion of the piston 20 and the end wall of the cylinder 10 is prevented.