To calculate the product number for ordering parts so that parts are not delivery, in case that a period for making a line empty is scheduled, in the empty line period for a time just before or just after this period.

In a day (10/3) before an empty line day (10/4), the number of products passing over an assembling point until the final product passes over the assembling point from the final delivery time (the circled number 2 in a column 52) is set as a product number for ordering parts at an ordering time corresponding to the final delivery time (60 pieces). In the day (10/5) after the empty line day, the L/O number of a time zone from the time when the first product put to the line reaches a product completion port (12:00) where the arrival time belongs to (50 pieces in a column 46). For the remaining time zone, the remaining L/O number is divided by the remaining time zone number to calculate the L/O number of the remaining time zone (100 pieces in a column 46).