An image is generated as exposing a surface to a scanning laser beam in accordance with the image forming process. The intermediate image transfer member receives the image from the image bearing member to transfer the image onto the recording sheet. The memory stores a plurality of values ​​of process line speeds B for defining a plurality of values ​​and the speed of the image transfer process of the process line speeds A for defining a speed of the image forming process in the sub-scanning direction. The controller combines the process line speeds A, B as to arbitrarily select a plurality of selectable values: a processing line speed of a plurality. Further, by another aspect, the voltage sensor detects a voltage of the photosensitive member, the toner attached to the detection sensor, and detecting the toner adhesion amount of the photosensitive member, a charging member provides a charge onto the photosensitive member, a grid adjusting member controlling a grid voltage of said charging member, a laser exposure unit exposes the photoconductor to a laser beam, the exposure adjustment member is to adjust the exposure amount of the laser beam, the development gamma detecting member is the developing gamma rays as to perform a continuous operation It detects a. Reference table includes information to determine the voltage after exposure of said photosensitive member in accordance with said development gamma rays obtained as a proper voltage value and the developing bias and the development gamma detecting member of the photosensitive member. Controller from said laser exposure unit to obtain the respective required voltage to be used as the detection voltages of the photosensitive body, and wherein the optimum value of the grid voltage of the charging member and said grid adjusting member to rotate to a process linear velocity of the respective in the laser beam exposure and the bias of the sense voltage is determined after the exposure voltage that is used as the exposure adjusting member, and by reference to the information which is contained in the reference table.