This paper reports the relation between readability and brightness of the printed paper based on the experimental result with eleven subjects whose acuity is from 0.5 to 1.5. The readability, the brightness and these relationships have relations to the visual acuity. The readability has relation to the scene of reading even if the visual angule of letter is the same. The brightness of task surface is independent of the difficulty of task. If the illuminance on the task maintains brightness at a feeling of satisfaction, it is satisfied the proper condition for reading.