The invention provides an aspect ratio discrimination apparatus and an image display apparatus which prevent a malfunction in discrimination of a first video signal for exhibition of a normal image and a second video signal for exhibition of a horizontally elongated image. An upper-lower portion average brightness calculation section receives an input video signal to form an image and calculates an average brightness of upper and lower portions (black band portions) of the image, and an upper-lower portion brightness difference calculation section calculates differences between the average brightness and brightness levels of the black portions of the image. A high brightness difference rate detection section discriminates whether or not the rate of the area of portions in the black portions in which the brightness differences are higher than a predetermined level is higher than a predetermined value. When it is discriminated that the rate of the area is higher than the predetermined value, it is discriminated that the video signal inputted to the aspect ratio discrimination apparatus or the image display apparatus has the aspect ratio of 4 : 3.