To set up the start and end dates of work related to important point management dates and to easily judge the start and end dates of the work from a process diagram by setting orderly relation with important point management dates to be important points in process management such as intermediate inspection and completion inspection in objective work restricted at its dates.

In the process network preparing method for dividing the whole construction necessary for constructing a structure into working units and expressing the order of respective working units and restriction relation of working relation by a network connected by rectangles and arrows, important point management dates are set on important points for process management in the network, the orderly relation is set between the important point management dates and working units to restrict the start date and end data of the work. If there is a work having to be completed up to a set important point management date or a work capable of being started only after a set important point management date, the start date or end data of the work is preferentially set in accordance with the set orderly relation.