An Expert System (ES) Shell (developed by Toshiba Corp.) which applies to the scheduling of production plan and operation plan is introduced. It describes that this tool is equipped with flowchart editor and constraint condition editor which mention the knowledge related to scheduling method, and that the former expresses scheduling procedure knowledge in the form of flowchart by combining basic tasks prepared beforehand, and the latter expresses constraint conditions which should be satisfied by the schedule, and knowledge related to the priority order which should be considered in-between in the form of IF-THEN Rule which is very close to Japanese. In addition, the knowledge is equipped with knowledge debugging system which conducts debugging while executing the knowledge. It adds that by using this tool, the manhour required for the development and maintenance of ES can be reduced considerably. 2 refs., 3 figs.