An image forming apparatus capable of changing over between black printing and color printing with an intermediate transfer belt being brought into contact with and separated from photoconductors by means of a black transfer member and a three-color-integrated color transfer member. The image forming apparatus has a registration mark former for forming registration marks on the intermediate transfer belt, a registration sensor for reading the registration marks, and a controller for controlling the registration mark former based on the registration marks read by the registration sensor, so as to adjust registration. The controller has an adjustment mode to adjust registration between black and color.