PURPOSE: To realize easy and high-speed retrieval through simple constitution by making a queue into two-hierarch structure, and executing scheduling by inserting tasks into only the queue of priority order when there are two or more tasks of the same priority.

CONSTITUTION: The control block 12 of the task stores a pointer 121 to constitute an exclusive queue to connect only a head task in the case that there are plural tasks in priority order and of the same priority and the pointer 122 to constitute the exclusive queue to connect plural tasks in the priority order and of the same priority in the order of arrival and the value 123 of the priority of the task. Accordingly, when there are two or more tasks of the same priority, by inserting them into only the queue of the priority order, only one task is allowed always to be located on the exclusive queue, and the high-speed retrieval of the queue can be executed. Thus, the high-speed retrieval of the queue is realized, and simultaneously, effect that the insertion and the removal of the task to the queue are remarkably simplified is obtained.