An image forming apparatus is provided which is of an electrophotographic type, and is capable of setting a gradation number of a patch pattern to be formed corresponding to various factor information, and to perform a process control. The image forming apparatus includes a patch pattern forming part to form a toner image of a patch pattern on an image carrier; a developing part to develop the patch pattern; a toner image density detecting part to measure a toner image density of the patch pattern; and a process control performing part to vary an image forming process condition based on detection results obtained from the toner image density detecting part, and to stabilize an image density.