1. A parts production scheduling method for preparing a production order schedule of parts necessary for the production of higher products after receipt of a production order schedule of the higher products, comprising the steps of: pre-registering parts identification information, inter-parts similarity information, and part-by-part production order pattern information; dividing the production order schedule of the parts into plural zones each equivalent to production of a predetermined number of consecutive products in the product order schedule of the higher products; shifting the production order schedule of the parts so that the production order schedule of the parts is ahead of the production order schedule of the higher products by one zone; for each zone of the production order schedule of the parts, converting parts to be produced on a parts production line into corresponding pieces of information of the pre-registered parts identification information; and for each zone of the production order schedule of the parts, sorting the converted pieces of parts identification information by the pre-registered inter-parts similarity information and collating the converted pieces of parts identification information with the pre-registered part-by-part production order pattern information.