A technique of enhancing attachment of a liquid supply unit to a liquid ejection device is provided. A first cartridge 100a and a second cartridge 100b are attached to a carriage 27 of a printing device 27 via a holder structure 200. The holder structure 200 has a lever member 230 rotated and moved to engage with a main engagement part 120 of each of the first and the second cartridges 100a and 100b. Each of the first and the second cartridges 100a and 100b has a first side wall portion 125 and a second side wall portion 126 configured to press the lever member 230 and rotate and move the lever member 230 forward in the course of attachment of the first or the second cartridge 100a or 100b to the holder structure 200. A rotation axis RX of the lever member 230 is located at a position closer to an ink supply port 110 or 110a than the first side wall portion 125 and the second side wall portion 126 in the course of attachment of the first or the second cartridge 100a or 100b.
