An equipment which requires an external unit to be assembled therein for starting inherent operation. The equipment includes a detection means for detecting an identification mark such as a trade mark affixed to the external unit. The equipment is only operable upon detection of a proper identification mark. The equipment may be a printer and an image recording apparatus such as a copying machine, and the external unit may be an image recording medium cassette such as an ink ribbon cassette and a rolled photosensitive sheet cartridge.