An image display device which is used to view an image by being worn on a head or a face, that is, a head-mounted display, has been generally used. In the head-mounted display, for example, an image display unit is disposed for each of the left and right eyes, and an enlarged virtual image of a displayed image is formed by a virtual image optical system, and thereby a user can observe an image with a sense of reality. Popularity of the head-mounted display is very high. As mass production proceeds from now on, every person might come to have one head-mounted display as cell phones, smart phones, and hand held game machines have spread.
The head-mounted display is equipped with display panels of high resolution made of, for example, a liquid crystal or an organic Electro-Luminescence (EL) element and the like as display units for the left and right eyes. In addition, the head-mounted display can be classified into a light-shielding type and a permeable type. The light-shielding head-mounted display is configured to directly cover the eyes of a user when worn on a head, and a sense of immersion is increased when the user views an image. A display screen is photographed in an enlarged manner using a virtual image optical system and is observed by a user as an enlarged virtual image which is at an appropriate angle of view, and it is possible to reproduce a sense of reality such as that when viewing in a movie theater when multi-channels are reproduced in a headset (for example, refer to PTL 1). On the other hand, in case of a transmitting head-mounted display, a user can view (that is, see-through) an external landscape over an image while wearing the head-mounted display and the image is displayed (for example, refer to PTL 2).
Whichever type between the light-shielding type and the permeable type the head-mounted display is, the head-mounted display draws a user wearing the head-mounted display into a virtual world. Therefore, it is of concern that sight and hearing of the user are slow to respond to the oat side world.
For example, a sight device which includes a function of stopping an image when an emergency button provided in a remote controller is pressed, and can be worn on a head has been proposed (for example, refer to PTL 3). However, a user of the sight device has to determine whether to stop an image or not by pressing the emergency button himself. That is, the user has to care about what is happening in the outside world while viewing an image, and receives interference from the real world, and a degree of immersion in a virtual world displayed by the sight device is lowered. Furthermore, if observing the outside world by pressing the emergency button to stop an image, there is an errand which is not important, thereby causing a disturbance in viewing an image.
In addition, a mounted display device which occupants of a car wear on the face to use is a device configured to detect an emergency state of the car, and detects a state in which a posture of the occupant becomes unstable or dangerous when a brake pedal is suddenly stepped on, steering is suddenly turned off, and the car collides with and rear-ends an object during a movement of the car as an emergency state to allow an outside world to be seen the detected emergency state has been proposed (for example, refer to PTL 4).
Moreover, an image display device which is worn on a face of a user and is equipped with a predetermined sensor to allow the outside world to be seen by instantly opening a shielding unit by a sudden movement, or an impact or a sound caused by an external factor has been proposed (for example, refer to PTL 5).