The respective jobs of copying, printing, scanning, and faxing processed by an integrated application are unitarily divided into four job steps. A package of function modules selectively used in the respective jobs is classified into four groups of input, create, edit, and output function modules according to the division. A data format is unified into bitmap by a create function module, and the bitmap data is processed by an edit function module for pagination or aggregation, etc. In response to receiving setting information and a job code, a job controlling module creates job step control blocks and writes the information therein to create a job. Each of job step controlling (JSC) modules to starts a function module for each page, and after the completion thereof, creates a thread control block for the next downstream side JSC module.