Sandwiched and coupled between the rear and face plates and constituting a vacuum container together with the rear and face plates; a high voltage introducing member for introducing a high voltage from a voltage source; and an independent wire which is electrically independent from the high voltage introducing member and formed surrounding a high voltage area in the vacuum container, wherein a resistor film is formed between the high voltage introducing member and the independent wire. The wire is formed inside and outside of the vacuum container and is connected to an earth potential.