Abstract: In a parallel processing system by an OS for single processors which operates an OS for single processors and an existing application for single processors on a multiprocessor to realize parallel processing by the multiprocessor with respect to the application, with the multiprocessor being logically divided into two groups of a first processor side and a second processor side, a unit of work that can be parallelized within the application operating on a processor on the first processor side is controlled as a new unit of work on a processor on the second processor side.