PURPOSE: To continue the glare preventing state for a long time without darkening the whole field of vision by providing a direction of incidence detecting device and a dimming controlling device and changing light transmittivity of a dimming plate locally by the two devices according to the direction of incident light.

CONSTITUTION: The device is provided with a direction on incidence detecting device 1 for detecting the direction of light incident to a dimming plate 3 and a dimming controlling device 4 that controls local transmittivity of the dimming plate 3. The dimming controlling device 4 includes an arithmetic circuit 41 such as a microprocessor etc. for making specified calculation, an ROM 42 (read-only memory) in which a memory to make the arithmetic circuit 41 perform specified calculation is stored, and an RAM 43 (any time write and read memory) that stores data etc. inputted from the direction of incidence detecting device 1 and a visual point position detecting device 2. Thus, glare prevention can be made effectively without darkening the whole field of vision. As dimming is limited to a part of the field of vision, glare prevention can be continued for a long time.