An image-forming method performed in an image forming apparatus which includes: a first memory, storing first information indicative of a first factor causing color shift; and a detachable process cartridge, provided with an image carrier and a second memory storing second information indicative of a second factor causing the color shift, the method including: reading out the first information and the second information when the image forming apparatus recognizes an attachment of the process cartridge, obtaining an estimated color shift caused by the first factor and the second factor, based on the first information and the second information; judging whether the estimated color shift is within a predetermined range; and performing an initialization of the process cartridge when it is judged that the estimated color shift is within the predetermined range.