An automatic transaction apparatus operates an automatic transaction unit using middleware whose environment is set by a kernel, which uses conventional middleware even if the interface with the host is standardized. The parameters specific to the vender of the apparatus are set in the parameter file in advance, the I/O control layer edits the parameters of the commands of a common interface (API) and the vender specific parameters of the parameter file, converts the result into the commands of the ATM middle API, sends them to the ATM middleware, and operates the vender specific I/O units.