A technique of enhancing attachment of a liquid supply unit to a liquid ejection device is provided. A first ink cartridge 100a and a second ink cartridge 100b are attached to a carriage 27 of a printing device 10 via a holder structure 200. Each of the first and the second ink cartridges 100a and 100b includes a circuit substrate 130 having a plurality of terminals 151 to 159 which are electrically connected with a device-side terminal assembly 250 provided on the holder structure 200. Each of the first and the second ink cartridges 100a and 100b also includes a main engagement part 120 configured to engage with a lever member 230 of the holder structure 200 as an engaged part, such as to limit motion of the circuit substrate 130 away from the holder structure 200. The circuit substrate 130 includes a first terminal 151 and a second terminal 152 located on respective ends in an array direction of the terminals. The main engagement part 120 has a width greater than an interval between contact portions CP of the first and the second terminals 151 and 152 in the array direction of the terminals.