PURPOSE: To obtain a synchronous production scheduling planning device possible to advance a delivery date by allotting each assembly time for a specific final product to the respective production lines by a unit of integer multiple of preset minimum work time in a manner of filling the rear along a sequence of arrangement.

CONSTITUTION: In a reference information setting part 71, an order of each process, work time of each process and a material holding amount of each process are registered in a reference data base 73. In an input order determining part 74, a planning objective data, consisting of a product name, completion desired date and a number of sets of manufacture, is input in each manufacture order with an input order determined by utilizing an input order determining knowledge data base 77. In a backward scheduling part 79, based on the process order and the work time shown by a process procedure, the work time, is allotted to empty periods of a per-process relative time allotting table 81 successively from the final process to the preceding process. In a planning evaluating part 83, by utilizing a planning actual result statistical data base 82, a schedule result, in which a required time between the processes is minimum and a rate of operation in the total process is maximum, is selected.