A photomask includes a transparent mask substrate, and a plurality of square mask cells provided on the mask substrate. Each mask cell includes at least one of a light transmitting region and a light shielding region. A planar region (in which the mask cells are formed) of the mask substrate includes a first region, a second region surrounding the first region, and a third region outside the second region. The first region includes a first group of mask cells transmitting lights of a first light intensity greater than zero and less than or equal to 1. The second region includes a second group of mask cells transmitting lights of a second light intensity greater than zero and less than the first light intensity. The third region includes a third group of mask cells transmitting lights of a third light intensity greater than or equal to zero and less than the second light intensity.