An image forming apparatus comprising: an image bearer to rotate; a toner image forming device to form a toner image on the image bearer, wherein the toner image forming device comprises: a charger to charge a surface of the image bearer; a latent image forming device to form a latent image on the image bearer; and a developing device to develop the latent image with developer; a transfer rotator disposed opposing to the image bearer; a transfer device to transfer the toner image from the image bearer onto either the transfer rotator or a recording medium conveyed on the transfer rotator; a rotation position detector (18; 70) to detect a reference rotation position of one of the image bearer and a rotator that contributes to image formation, wherein the rotator comprises at least one of a developer bear to bear developer thereon and a sheet conveyor to oppose to the transfer rotator and to transport the recording medium thereon; an image density detector to detect an image density of the toner image transferred from the image bearer; characterised in that the image forming apparatus is constituted to: cause the toner image forming device to form an adjustment toner image equal to or greater in length than the image bearer in a rotation direction of the image bearer, cause a linear velocity difference between the image bearer and the transfer rotator in transfer of the adjustment toner image, and acquire, from a detection result of the adjustment toner image generated by the image density detector, image density unevenness data with reference to detection of the reference rotation position, the image density unevenness data including an image density unevenness component having a rotation cycle of the one of the image bearer and the rotator, and adjust an image forming condition including an operating condition of at least one of the charger, the latent image forming device, and the developing device according to the detection of the reference rotation position, the image density unevenness data, and the linear velocity difference. an image bearer to rotate; a toner image forming device to form a toner image on the image bearer, wherein the toner image forming device comprises: a charger to charge a surface of the image bearer; a latent image forming device to form a latent image on the image bearer; and a developing device to develop the latent image with developer; a charger to charge a surface of the image bearer; a latent image forming device to form a latent image on the image bearer; and a developing device to develop the latent image with developer; a transfer rotator disposed opposing to the image bearer; a transfer device to transfer the toner image from the image bearer onto either the transfer rotator or a recording medium conveyed on the transfer rotator; a rotation position detector (18; 70) to detect a reference rotation position of one of the image bearer and a rotator that contributes to image formation, wherein the rotator comprises at least one of a developer bear to bear developer thereon and a sheet conveyor to oppose to the transfer rotator and to transport the recording medium thereon; an image density detector to detect an image density of the toner image transferred from the image bearer; characterised in that the image forming apparatus is constituted to: cause the toner image forming device to form an adjustment toner image equal to or greater in length than the image bearer in a rotation direction of the image bearer, cause a linear velocity difference between the image bearer and the transfer rotator in transfer of the adjustment toner image, and acquire, from a detection result of the adjustment toner image generated by the image density detector, image density unevenness data with reference to detection of the reference rotation position, the image density unevenness data including an image density unevenness component having a rotation cycle of the one of the image bearer and the rotator, and adjust an image forming condition including an operating condition of at least one of the charger, the latent image forming device, and the developing device according to the detection of the reference rotation position, the image density unevenness data, and the linear velocity difference. cause the toner image forming device to form an adjustment toner image equal to or greater in length than the image bearer in a rotation direction of the image bearer, cause a linear velocity difference between the image bearer and the transfer rotator in transfer of the adjustment toner image, and acquire, from a detection result of the adjustment toner image generated by the image density detector, image density unevenness data with reference to detection of the reference rotation position, the image density unevenness data including an image density unevenness component having a rotation cycle of the one of the image bearer and the rotator, and adjust an image forming condition including an operating condition of at least one of the charger, the latent image forming device, and the developing device according to the detection of the reference rotation position, the image density unevenness data, and the linear velocity difference.