Present invention provides an image forming apparatus capable of forming an image on various kinds of photosensitive material by subjecting the photosensitive material to an image forming process having at least imagewise exposing, developing, and fixing process on a process condition determined in accordance with a kind of the photosensitive material. While processing certain kind of photosensitive material, a kind discriminator detects a new kind of photosensitive material being subjected a current image forming process, CPU inhibits a new image forming process until judging a predetermined process of the current image forming process as being completed from a signal of a process monitor.