An organic insulator is composed an organic resin phase as a main component. The organic resin phase includes a weather-resistant stabilizer. The organic resin phase includes an inner region and a surface region formed in at least one surface of the inner region. The surface region has a higher content ratio of the weather-resistance stabilizer than the inner region. A metal-clad laminate includes the organic insulator and a metallic foil laminated on at least one surface of the organic insulator. A wiring board includes a plurality of insulating layers composed of the organic insulator, and a metallic foil disposed between the insulating layers.