1. A method for parallel execution of processes in a multiprocessor system having a plurality of instruction processors for converting a source program written in a high-level language into an object module and for processing a parallel-executable object segment in parallel by creating and executing parallel processes on the plurality of instruction processors, said method comprising the steps of: setting a run cost value for providing the object module with a basis for a serial run time for the parallel-executable object segment in the object module; determining the number of parallel processes to be created from the object segment by dividing the run cost value by an overhead value for executing parallel processing rather than serial processing of the object segment; creating the determined number of parallel processes from the object segment; registering the created parallel processes in a queue; fetching the created parallel processes from the queue and assigning the parallel processes to ones of said plurality of instruction processors; and executing the parallel processes using the plurality of instruction processors in accordance with the overhead value corresponding to the parallel processing except when the run cost value is substantially equal to the overhead value and serial processes are, therefore, executed.