PURPOSE: To obtain a system call execution method which correctly operates as against all system call execution requests by permitting a system call server to automatically execute a system call rotating a ready queue after the execution of the system call.

CONSTITUTION: When a task or an interruption handler issues the system call, an operating system transmits the system call execution request to the system call server. The system call server receives the system call execution request (ST100), and alternatively executes the system call which is issued in accordance with the system call execution request instead of the task or the interruption handier issuing the system call (ST200). Then, the system call server rotates a task string having the same priority as the system call server in the ready queue in a head direction. Namely, the system call server positioned at a head in the task string is shifted to the trailing end of the same task string (ST400).