The image forming apparatus includes a rotary belt member; a detector for detecting a position in a rotating direction of the belt member; a toner image forming device for forming a toner image at a predetermined position on the belt member based on a detection signal of the detector; and a recognition device for recognizing the type of belt member based on the detection signal. The apparatus is stopped or the information related to the belt member is notified based on the recognition result of the recognition device. Thus, by a simple configuration, failures caused by an unsuitable rotary belt member can be easily prevented.