Then all the photoreceptors 222 a, 222 b, 222 c and 222 d are driven to rotate to implement charging, development and other necessary operations for each of the photoreceptors 222 a, 222 b, 222 c and 222 d, in accordance with the electrophotographic process (S3), whereby a color image is formed on a sheet of paper. [0103] On the other hand, when black/white image output mode is selected (N at S1),