Abstract: A seismic isolator comprises: a friction device having upper friction plate and a lower friction plate, a friction plane of the upper friction plate and the lower friction plate having a characteristic of Coulomb friction; and horizontally placed springs which reduce a relative displacement and a residual displacement. The upper friction plate includes being any one selected from the group consisting of a polyacetal resin containing lubricating oil, a bronze or brass alloy with solid lubricant buried therein, a sintered alloy with solid lubricant dispersed therein, a porous structure of cast iron with lubricant oil contained therein and a steel backing sintered layer with solid lubricant and oil impregnated therein. Furthermore, the lower friction plate includes being any one surface-treated material selected from the group consisting of a hard chromium-plated plate and a hard nickel-plated plate.