The present invention is a method for improving the visibility of an image display device capable of obtaining an image display device having excellent anti-reflection performance and spot contrast even when an optical laminate having a light-transmitting substrate having a birefringence in the same surface as a polyester film is used. Gives To this end, the present invention is a method for improving the visibility of an image display device having an optical laminate having an optical functional layer on one surface of a light-transmitting substrate having a birefringence in the surface, the ground having a large refractive index of the light-transmitting substrate There is provided a method for improving visibility of an image display device, wherein the optical stack is arranged such that the axis and the vertical direction of the display screen of the image display device are parallel.