To confirm and check the expected date of the final completion of a product by calculating completion periods of an ordered article by operation processes and also calculating the cumulative value of standby times between the respective operation processes, and adding it to the cumulative value of the operation times of the respective operation processes and calculating the final completion expected date.

Process information and operation department information on the operation processes by ordered articles are recorded in an operation process and operation department information file 2 on a host computer 1, the operation processes and standard operation periods are recorded in a standard operation time recording file 3, and backlog workloads and backlog workload end expected periods of the respective operation processes are recorded in a workload information recording file 4. When information on an ordered article is inputted to the host computer 1 through an on-line terminal machine 7, an operation process is specified according to the operation process and operation department information file 2 to calculate ordered article completion periods by operation processes, which are added to the cumulative value of the operation times of the operation processes, thereby calculating the final completion expected date.