PURPOSE: To display visual field environment in consideration of the state of adaption of the eye to brightness by measuring the brightness in the visual field environment and controlling image brightness and the brightness of a light source device based on the measured value.

CONSTITUTION: An image generating device 5 generates a visual field environment image in operation and an image display device 1 shows the image to an observer. The light source device 2 is installed so that the light source is not put in the visual field of the observer, and the observer is given with equivalent light curtain brightness. A brightness controller 3 sends commands to the image display device 1 and light source device 2 according to the brightness that a brightness measuring instrument 4 measures to control the image brightness on a screen 1b and the brightness of the light source device 2. Consequently, the state of adaption wherein the image is seen in the same state of the adaption of the eye in brightness conditions which can not be displayed on the screen 1b of the image display device 1 can be simulated on the screen 1b within a realizable range.