1. An image display apparatus comprising: a characteristic value calculating unit that calculates brightness-related image characteristic values of at least one of right-eye image data and left-eye image data that form stereoscopic image data; a expanding coefficient calculating unit that calculates a expanding coefficient common to the right-eye image data and the left-eye image data based on the image characteristic values calculated by the characteristic value calculating unit; a brightness expanding unit that performs brightness expanding on both the right-eye image data and the left-eye image data by using the expanding coefficient calculated by the expanding coefficient calculating unit; and an image display unit that displays an image based on the right-eye image data and the left-eye image data having undergone the brightness expanding.