Abstract: In this paper, the changes of the resistance and the electron gain of the CEM after bake-out at different temperatures and treatment with Cs are examined. It is found, that the transition temperature of the resistance from reversible change into irreversible is 250℃ or higher. A method of determining the optimum gain of the CEM during heating by means of measuring the resistance changes is proposed. The damaging action of Cs to CEM is investigated and proper protecting means is proposed. It is shown, that the method of convering two ends of the CEM with nickel caps is an effective one for preventing the CEM from being damaged by Cs during Cs treatment.