To automatically avoid saturation or insufficiency of measurement results of an optical sensor when image quality is corrected on the basis of the measurement results, and also automatically diagnose a breakdown of the optical sensor.

An image display apparatus comprises: an optical sensor 20 to measure ambient light; an image quality correction section 104 to correct image quality; a display section 105 to display image information; and a control section 107 to control individual component elements. The control section 107 controls the image quality correction section 104 in terms of the image quality including brightness and color thickness of the image information, on the basis of measurement results of the optical sensor 20. Further, when the measured values as the measurement results of the optical sensor 20 are in a saturated or insufficient state that corresponds to a measurable maximum or minimum value, the control section 107 avoids the saturated or insufficient state by controlling a measuring time of the ambient light so as to automatically decrease or increase. The measured values obtained by the optical sensor 20 are integrated values of values measured at predetermined sampling intervals and the number of sampling operations. The measuring time is time determined by the sampling intervals and the number of sampling operations.