A communication system that includes multiple conferencing devices connected in a daisy-chain configuration is communicably connected to far-end conference participants. A determination part determines whether the calculated total value of the data amount exceeds a permissible value which has been set in advance according to a predetermined capacity of a reception data memory. A rotary knob with several stop surfaces selects an upper limit on the pivot range of the lever and the adjustment height of the adjusting roller. One or more flow disturbances emanating downstream from the protrusion are deflected using the at least one reduced pressure zone. A lower polarization plate is arranged on the lower substrate, and a lower compensation film such as a scattering sheet and a prism sheet is arranged on the lower polarization plate. The separator 13 has an average pore size of 0.