A toner cartridge memory for detecting a toner cartridge information item is provided to shield a read/write circuit substrate from the outside. If the read/write circuit substrate is shielded from the outside, a shield member is anew installed, thus leading to an increase in the manufacturing cost of the relevant image forming apparatus. In order to shield a radiant noise with a simple arrangement, an image forming apparatus is provided which includes a unit detachably mountable on a main assembly, the unit having at least an image bearing member and a memory; an image writing unit for writing an image on the image bearing member in accordance with an image information; and a communication unit for communicating with the memory, in which the communication unit is arranged under the image writing unit; and the image writing unit functions to shield the: radiant noise emitted from the communication unit.