An ink cartridge, which is releasably installed to a cartridge-installing section, includes a contact section which is brought into contact with the cartridge-installing section when the ink cartridge is installed to the cartridge-installing section, a stress light-emitting section which is provided with the contact section and which emits light by receiving a force when the contact section is brought into contact with the cartridge-installing section, and a light-receiving sensor which receives the light emitted by the stress light-emitting section and which generates a detection signal to indicate detection that the ink cartridge is installed. Accordingly, an attaching mechanism is provided, which is capable of detecting whether or not the ink cartridge is installed appropriately.