PURPOSE: To prevent a sense of unease from being caused by preventing a carrying person from being a state of blindfold when any fault such as video image non-display or a power failure takes place.

CONSTITUTION: Based on a signal from a video output device 3, when a controller 2 discriminates it that no video signal is outputted, a drive voltage is not outputted to an electronic shutter 8 to make it bright so as to allow the carrying person to observe an external image. Conversely when it is discriminated that the video signal is outputted, a drive voltage is outputted to the electronic shutter 8 to set it to a dark state thereby interrupting an external light and allowing the carrying person to observe an electronic video image displayed on a liquid crystal display device 13.