An actively controlled colloidal damper having controllable damping characteristics. The damper has a cylinder (2); a piston (4) reciprocatably guided and supported by the cylinder (2) and forming a closed space (3) in cooperation with the cylinder (2); a porous body (8) having a large number of fine holes and received in the closed space (3); operation liquid (7) received in the closed space (3) together with the porous body (8), flowing into the fine holes in the porous body (8) when the pressure in the closed space (3) is increased, and flowing out of the fine holes when the pressure in the closed space (3) is decreased, and pressure regulation means, such as a servo value (6) and a pump device (10), for regulating the pressure in the closed space (3).