The process control system converts, into images, time-varying waveforms of inspection data of an assembled product, parts, and sub-assembling processes that constitute the assembling process, performs matching between an inspection waveform image (IWI) of the assembled product and a predetermined deterioration pattern image (DPI), determines whether IWI of the assembled product is similar to DPI, performs, when IWI is similar to DPI, a first determination for performing matching between an IWI of each of sub-assembling processes and DPI and determining whether there is a sub-assembling process similar to DPI, performs, when there is a sub-assembling process similar to DPI in the first determination, a second determination for performing matching between IWI of each of parts assembled in the sub-assembling process similar to DPI and DPI and determining whether there is a part similar to DPI, and specifies a deterioration factor based on results of the first and second determinations.