PURPOSE: To reduce the memory used for schedule preparation by scheduling only a lot which is high in priority or importance firstly and preparing a long- period process schedule, and preparing an artificial process schedule for a lot which is low is priority or importance.

CONSTITUTION: For the progress control lot which is high in priority or importance, a scheduler 1 recognized a process completion final process from a lot control table 15 so as to control the completion day and a schedule preparing part 11 schedules following process by referring to an operation sheet 13 and the operation schedule 12 of devices to prepare the process schedule 14. For the lot which is low in priority or importance, on the other hand, an artificial schedule preparing part 10 is actuated to extract necessary parts from the operation sheet 13 and prepare the artificial process schedule. This system excludes the progress noncontrol lot which is low in importance from the schedule, so it need be stored as scheduling information and the time and memory required for the schedule preparation are reducible.