To provide a production planning system that a planner can easily recognize the changes of unofficially notified value and determined value, the reliability can be improved while sufficiently reflecting the difference of changes in a production plan and the planning cost can be reduced.

The comparator part 22 of an order part 14 in the production planning system 10 recognizes the differential amount of a determined value from an unofficially notified value and when the value is out of a set allowable range, an alarm is issued. Besides, a plan reflecting part 24 calculates, the production plan of only the differential amount, adds it to the production plan prepared in the last and plans the production in which the differential amount has been reflected while simplifying production planning.