According to the present invention, there is provided a holding mechanism of an object to be processed W, which comprises a relay switch to electrically disconnect a detection circuit having the function of detecting the stripped state of a protective film of a lower electrode and removing a residual charge from the direct-current component in a high-frequency power supply line from the power source supply line and which disconnects the detection circuit from the lower electrode in accordance with a process condition to prevent abnormal electric discharge and which electrically connects the detection circuit to the lower electrode to detect the stripped state (life) of the protective film of the lower electrode from the direct-current component in a plasma discharge or to remove a charge into the lower electrode or a residual charge during plasma processing under a process condition not causing abnormal electric discharge or at maintenance time.