An attachment is mounted on a cartridge holder of a printer as a replacement of an ink cartridge. An ink outlet member having a link passage is separably secured to an attachment body. Ink is supplied from the exterior to the ink outlet member through an ink supply tube. When the attachment is mounted on the cartridge holder, a downstream end of the ink outlet member is positioned with respect to and connected to an ink supply needle of the printer. Accordingly, the attachment is easily and quickly installed in a liquid ejection apparatus. This reduces costs and makes it easy to use the attachment.