A memory card as an external connection device connected to an information processing apparatus such as a computer as a host device. The memory card (1) includes a register circuit (13), a data buffer circuit (14), a memory I/F controller (16), and a flash memory (17). The register circuit (13) and the data buffer circuit (14) are accessed by the host device by using a command (TPC) defined by the transfer protocol. The TPC contains an extended command for simultaneously transferring a parameter to be store in the register circuit (13) and a control instruction to be given to the memory I/F controller (16).