To easily perform positional adjustment of the line of a sight detecting means with respect to the eyeball of an observer, while a displaying means for exclusive use for displaying the image of the eyeball is dispensed with.

When a line of sight detecting means, which provides a projector for illuminating an eyeball and an image capture part for capturing the image of the eyeball and detects the watch point of a subject, by using the above described image of the eyeball is fixed to the eyeball of an observer observing an image displaying means 3, a control means which captures the image of the eyeball obtd. by this image capturing part and displays this image of the eyeball on the displaying means 3 and performs positional adjustment of the line of sight detecting means to the eyeball is provided.