The image forming apparatus forms an image on a surface of a recording medium by using ink and treatment liquid. The hub assembly includes a magnet and a coil that are both internal to the hub. 3 or higher when the electrophotographic photoreceptor is charged to a charged potential absolute value of 500 V and then irradiated with a monochromatic light of the same wavelength as that of the light beams to decay the charged potential absolute value to 250 V. In short, one data processor can use in common the peripheral resources of the other data processor.