PURPOSE: To prepare a process plan figure even when it is difficult to decide a schedule condition down to every detail, and to easily cope with the change of the process plan.

CONSTITUTION: An outline process network preparing part 24 provided at an outputting part 40 of a computer 10 retrieves data based on a past process network stored in a structure data storage part 30, based on the data of the process plan to be newly prepared inputted from an inputting part 50, selects a working process corresponding to the newly inputted working process, and prepares an outline process network. Then, a network correcting part 25 corrects the outline process network by using the knowledge of an expert stored in a rule storage part 31, and prepares the detail process network of a new construction.