PURPOSE: To improve the using efficiency of a memory space by forming a storage address specifying table specifying an address space storing the information volume of each I/O apparatus in a memory of a computer.

CONSTITUTION: The storage address specifying table previously stored in a memory of a CPU6 in a computer 1 is sent to a DMAIF11 in an IF device 3 through a DMA interface IF8 and read in a memory in an arithmetic unit MPU9 through a bus 13 to process information from the I/O apparatus 2. When the information from the I/O apparatus 2 is inputted to the MPU9 through an apparatus IF12 under said status, the I/O apparatus sending the information is decided and the storage address specifying table is retrieved to specify the specification address. Subsequently, the inputted information is stored in a memory address in the CPU6 which corresponds to the specification address. Thus, the information in the apparatus 2 is stored in the specified minimum memory space in accordance with each maximum information volume of each master or local station.