Image display system and image display device

The present invention provides a technique for supplying appropriate image quality to a user. Upon executing an application, a PC1 outputs an automatic adjustment start signal s1 which is information relating to image quality required for the application, and on the basis of the automatic adjustment start signal s1, a display device 4 adjusts the image quality. Thus, it is possible to display an image with image quality suitable for each of the applications without causing any time-consuming manual operations by the user. Consequently, it is possible to provide appropriate image quality to the user.