PURPOSE: To provide the control method for process priority so that the priority of another process can be controlled in the operating system (OS) of a computer.

CONSTITUTION: A calculation expression to calculate the process priority, namely, the process priority expressed by process priority = (latest CPU using condition/constant) + (basic user priority) + (priority class value) is controlled by changing the priority class value peculiarly held in each process not concerning not only the own process (process A) but also the other process (process B). Thus, the scheduling of processes can be more optimized, and the flexibility of a system manager to the management of processes can be improved.