An overvoltage protector includes a first discharging electrode, a second discharging electrode, and an overvoltage protection part provided between the first and second discharging electrodes. The overvoltage protecting part has an insulating property under a normal operation condition, and has a conductive property if an overvoltage is applied between the first and second discharging electrodes. The overvoltage protecting part is made of a mixture of resin having an insulation property, an inorganic compound having an insulating property, and metallic boride compound powder. The metallic boride compound powder has a high melting point therefore it is hardly melted. Under high temperatures causing the powder to melt, the powder is oxidized and loses conductivity, thus providing a high reliability.