a ballast resistor device for use in a gas laser system for stabilizing the operation of the gas laser includes a housing , a ballast resistor element and a filler material filled in the space between the housing and the resistor element is provided . in the preferred embodiment , the filler material is substantially high in dielectric breakdown strength as well as in thermal conductivity , so that the ballast resistor device of the present invention has a rigid structure providing a strong mechanical and electrical durability , not to mention an excellent heat dissipating characteristic thereby allowing to prevent the resistor element from being overheated .