Any untransferred toners residual on the photosensitive drums 2 a, 2 b, 2 c and 2 d when the above-described images have been transferred from the photosensitive drums to the transfer material are removed and collected by the drum cleaning devices 5 a, 5 b, 5 c and 5 d. (2) Tandem Fixing Unit 41 FIG. 3 is an enlarged view of the tandem fixing unit 41 portion in the image forming apparatus of FIG.