PURPOSE: To improve operability by automatically generating a corresponding channel number by selecting an input/output device number and then displaying the channel utilization rate on a screen together with the input/output device number.

CONSTITUTION: A screen (definition 'screen') where a list of input/output device numbers 102 and their channel numbers 103 are made to correspond to each other is offered, and all channel numbers 103n for access to one or plural input/ output device numbers 102 are generated automatically by selecting the input/ output device numbers 102 on the screen and incorporated in the display. Then the input/output device numbers 102 selected on the definition screen, the channel numbers 103 which are generated automatically, and the number of an input/ output device in the channel when present are combined and grouped in input/ output controller units or larger control units, and they are edited in an easy- to-see state and displayed in the screen. Consequently, the display becomes easy to see, the specification is facilitated, and trouble for the display is eliminat ed.