Some kinds of the electrical cables and elastomer/plastomer materials, though having high outgassing rates, are occasionally used in a high vacuum system. In order to evaluate the ultimate pressure of the system in which those materials are to be installed, their outgassing rates have been measured as a function of pumping time by a through-put method. The outgassing rates of the cables and glass-fiber sleevings ranged from 10^-9 to 10^-5 Pa·m³. s^-1. m^-1 at 100 h, depending on the insulation materials or varnishing treatment. From the tests of the elastomer/plastomer materials, it was ascertained that the organic materials give high outgassing rates of the orders of 10^-5 to 10^-3 Pa·m³·s^-1·m^-2 at 100 h.