In regard to a scheduling method in a multithreading processor, a thread to be executed is dynamically selected from the threads allotted to the context units according to an operation state of the multithreading processor, and the number of threads to be executed simultaneously or the combination thereof is changed. Also, at the time of context switching, threads to be allotted to the context units are dynamically selected according to an operation state of the multithreading processor. As an example of a method for deciding the operation state, the decision is made by whether a set reference value is exceeded by the number of fetch stall times in a predetermined period on a thread-by-thread basis, number of missing cache times, memory access latency, IPC counter, or the like.