Abstract: In an assignment of input-output memory space for selectively assigning a plurality of the input-output devices to be connected to a computer to the input-output memory space in a predetermined range, after a signal train data group including a combination of signal train data deliberately determined for every system of a computer to be used and signal train data at a time when a system is set up by any of the plurality of input-output devices is written in a storage area of the input-output device for assignment, the signal train data group is compared with a signal train data group previously stored in the input-output device. Only when they coincide with each other, an address assigned to said input-output device is written and held in the storage area.