Provided is a colloidal damper capable of harvesting electrical energy—that is, practical electrical power—from mechanical energy acting from the outside. This colloidal damper has: a cylinder; a piston which is guided and supported so as to reciprocate freely within this cylinder, and which combines with the cylinder to form a sealed space; a porous body having many pores and housed within the sealed space; an operating fluid which is housed together with the porous body in the sealed space and flows into the pores of the porous body when pressure is applied, and flows out from the pores of the porous body when the pressure is reduced; and a piezoelectric element installed in the sealed space.