PURPOSE: To improve the universal usability of a buffer by not only preventing so-called operational lag in the regulation of a damping force, but also enabling the stepless smooth regulation of the damping force and simplifying the construction of the buffer itself while blocking the cost increase due to the utilization of expensive parts and the increase of the number of useless parts.

CONSTITUTION: While the rod side chamber R1 and piston side chamber R2 are filled with electric viscous fluid, both chambers communicate to each other through a communicating hole provided in a hollow piston rod 3, controlling gap S, communicating hole provided in a pipe body 4 and the pipe body. While the hollow piston rod 3 is one electrode member, the pipe body 4 is the other electrode member. A buffer is constituted such that when voltage is applied across both electrode members, the viscosity of the electric viscous fluid interposed in the controlling gap S is regulated.