PURPOSE: To change system configuration any time during operations without stopping a system by displaying file reference enable or disable while referring to a data file provided with system constitutive elements, controlling system constitutive element change enable or disable and executing the work.

CONSTITUTION: A file reference control means 30 sets file reference enable/ disable display 32 to the state of 'disable' and reports 'switch enable' through a file change control means 40 to a file changing means 50. After the means 50 switches use file display 62 in a file change means 60 to the side of new information, 'switch completion' is reported through the file change control means 40 to the file reference control means 30. The file reference control means 30 sets the file reference enable/disable display 32 to the state of 'enable' and a file referring means 20 refers to information changed from new information 68 through the use file display 62. Thus, system constitutive information can be changed without stopping the operations.