A scheduling method for use with a multi-thread system which is capable of time-sharing processing a plurality of threads is provided which can avoid the drawback of priority inversion, minimize the modification of a wait queue, and ensure the optimum use of the processing time of a CPU. According to the present invention, a time slot data is assigned to each thread and the scheduling is carried out on the basis of the time slot data. As a processing time is imparted to the time slot data, the execution of the thread to which the time slot data is assigned is started. In case that a higher priority thread has to wait for the completion of the execution of a lower priority thread, the time slot data assigned to the higher priority thread is handled as a time slot data of the lower priority thread, hence allowing the execution of the lower priority thread to be started upon a processing time imparted to the time slot data.