To allow a device to simply and quickly evaluate resolution.

In a medium that stores an image to be generated with a width smaller than a positive integer multiple of pixel pitch (p) of image data by a k% of the pixel pitch, a plurality of transparent parts of the medium through which an exposure light exposing the medium is transmitted have a pitch of M×p (M is an integer being 2 or over) and opaque parts each between the transparent parts having a width not smaller than the pixel pitch (p) are formed as an array. Then in a thin plate for evaluation purpose with K sets of transparent part groups each including a plurality of number of transparent parts, a distance from a transparent part formed closest to one end of a 1st transparent part group formed closest to the one end to a transparent part formed closest to one end of an n-th transparent part group formed closest to an n-th order (n is an integer being 2 or over and K or below) transparent part group is selected to be a prescribed value.