An I/O prescription table (1/0 PTBL) (20-1, 21) is associated with a processing program module (10-2, 11) that is executed by a conventional sequential execution type processor (10-1, 51). Each processing program module fetches the input data according to its associated 1/0 PTBL and stores the output data in the same table. An execution control program (30-2, 31) makes reference to the I/O PTBL associated with the processing program module of which the execution is finished, updates the designated I/O PTBL so as to indicate that the corresponding input data is prepared, and starts the processing program module associated with the I/O PTBL which is furnished with all of the necessary input data.