An image forming apparatus or a cartridge detachably attachable to the image forming apparatus is provided, wherein the apparatus comprises developer container for containing developer, developer amount detecting means for detecting an amount of the developer contained in the developer container, a memory for memorizing information concerning the amount of the developer detected by the detecting means and output means for outputting the information concerning the amount of the developer, and the output means outputs the information concerning the developer memorized in the memory until the detection result of the detecting means is confirmed.