no second development toner mixed into the first image and the second image had the reflection density of more than 1 4 as in the second embodiment however when the developer supply was set too high a relatively large amount of carrier was found attaching between the lines in the high frequency line image this is considered due to the fact that the excited phenomenon of flying carrier produces greater opportunities for the upper layer of the developer to come into contact with the surface of the photosensitive body 11 in this embodiment a magnet roll 173 incorporated in the second development processor 17 as shown in fig1 and 14 has development promotion magnets s1 39 n1 39 installed in a roughly central part between the predevelopment and postdevelopment magnetic poles s1 and n1 in this embodiment at the center in the effective development area m corresponding to the point closest to the photosensitive body 11 using this magnet roll 173 an image was formed under the same conditions as the second embodiment the second development toner did not mix into the first image and the second image produced the reflection density of more than 1 4 relatively large amounts of carrier were observed adhering between the lines in the high frequency line image in this embodiment 2 line pairs mm in the second development processor 17 in this embodiment a magnet roll 173 has the development promotion magnetic poles s1 39 n1 39 installed in the downstream portion of the effective development area m as shown in fig1 and 16 using this magnet roll 173 an image was formed under the same conditions as the second embodiment the second development toner did not mix into the first image and the second image produced the reflection.