The production of semiconductor devices manufactured through a plurality
of manufacturing sites is unitarily managed and an appropriate production
plan is instructed. A computer projects a production plan of an entire
company based on various information. The production plan is provided to
each manufacturing site as a production instruction and provided to each
business person or customer as a storing reply or an order accepting
period reply. If the projected production plan (possible production
volume) does not coincide with a production plan (necessary production
volume), parameters obtained by correcting production allocation,
production capability, lead time, yield and the like are re-input from a
parameter input terminal. Based on the corrected parameters, the computer
re-projects the production plan and projects an optimum production plan.