Abstract: A production reservation system is provided with an estimate supporting system and a generating part of a production reservation calendar. A sales department inputs order information in the estimate supporting system. A production time period in a production department is reserved in the generating part of the production reservation calendar in response to the order information entered in the estimate supporting system. The generating part of the production reservation calendar contains a delivery appointed date calendar and a manufacture date calendar. While using order data of an order information system which stores thereinto a change in order information, the production reservation system reserves and confirms a manufacture time period of a production line at an earlier stage.