The present invention relates to an HDMI system, and more particularly, to a method for setting mute flag in connection with transmission of audio data and auxiliary data transmitted through HDMI system, and an HDMI system using the same method. A support member has a first vent opening for enabling flow of inflation fluid away from the bag. In particular, groove portions for performing cascade multiplication of electrons from the photocathode are provided in the electron multiplier section, and on the respective surfaces of each pair of wall portions that define the groove portions are provided with one or more protrusions each having a secondary electron emitting surface formed on the surface thereof.