The present invention provides a production control system of enhanced efficiency which is adapted to a mixed production line wherein products having different specifications are mass produced by assembling different parts on a common assembly line. This system is used in a factory wherein different products are required for steps of production. As a result, a production control plan can be scheduled in consideration of part transport times between production factories. To this end, the production control system corrects for the required number, transport time, and final production plan schedule. The final production plane schedule is adapted to establish a production ratio that is an integral number in each of feed cycles in a revolution of the assembly line. To this end, unreserved areas are provided in the feed cycles.