Stored reference patch data are outputted, and a gray level of the reference patches obtained by scanning the outputted reference patches is compared with a reference level, such that a conversion table for storing gray level setting information is modified according to the comparison result. A driving condition of a light source for the light exposure is set by a user interface to newly set a print density of an image forming apparatus. Moreover, prior to the user setting, test printing is performed and the print density can be set according to a result of the test printing.