An ink cartridge has a memory controller that controls a series of processing that involves rewriting data into a memory. The memory stores information regarding the ink cartridge, for example, a residual quantity of ink in the ink cartridge. A control unit of a printer gives the ink cartridge an instruction including a specified address to execute an operation of rewriting the data in the memory (either an operation of erasing the existing data from the memory or an operation of writing data into the memory). In response to the given instruction, the memory controller rewrites the data at the specified address in the memory and sends back a response signal or an acknowledgement representing completion of the rewriting operation, together with address-related information corresponding to the specified address. The control unit receives the address-related information and verifies whether data has been rewritten correctly at a right address. This arrangement ensures a sufficiently high reliability in the operation of rewriting data into the memory.