PURPOSE: To provide a manufacturing plan generating device which can flexibly deal with the unexpected limit conditions end also can facilitate its development and maintenance.

CONSTITUTION: A manufacturing plan generating device contains in its main body 1 a simulator 11 and an inference engine 12 which are separate from each other. If a conflict occurs among the conflicting elements during the simulation, the simulator 11 interrupts execution of the simulation and sends an inference request to the engine 12. Receiving the request, the engine 12 performs a fuzzy inference to send the simulation executing sequence to the simulator 11 as a countermeasure to resolve the conflict. The simulator 11 receives the simulation priority and resolves the conflict of the conflicting elements based on the priority. Thus the simulator 11 carries on the simultation and outputs the simulation result.