To provide the production planning method which can speedily generate an ordering plan and a manufacture plan corresponding to changes of orders, the production planning system which is used for its implementation, and the device-readable recording medium where programs for them are recorded.

A delivery information generation part 19 generates delivery information according to the ordering plan and supply periods of respective materials and updates delivery information in a delivery information data base 4 into the generated delivery information. A long-period process plan correction part 25 puts unit orders assigned to a short-period Gantt chart together by orders that the unit orders belong to generate a partial manufacture plant corresponding to a long-period Gantt chart, rewrites the plant for the period corresponding to the short-period Gantt chart in a long-period Gantt chart stored in a memory 23 into the generated partial manufacture plan to correct the long-period Gantt chart, and updates a long-period Gantt chart registered in the process programming data base 3 into the long-period Gantt chart.