To provide a quality control method for presuming effectively reaction lots generating the cause of abnormal quality by clarifying the mixing ratio of the reaction lots to a product and presuming efficiently which of the reaction lots generates the cause of the abnormal quality in a manufacturing method using a batch reactor and a storage tank.

The mixing ratio of respective reaction lots to a product is found by (1) selecting a newest lot, (2) setting the initial value of the 'unspecified ratio' of parameters at 100%. and (3) finding the mixing ratio (%) in a storage tank and selecting reactions lots by the formula of unspecified ratio (%) X (introduced amount/content amount of storage tank after introduction). Then (4) the unspecified ratio (4) = unspecified ratio (%)-mixing ration (%) is computed, and (5) the selected reaction lots and the mixing ratio thereof are stored (6). The unspecified ratio found in (4) is compared with a parameter for discontinuing the computation to complete the computation, or whether selecting a new reaction lot returning to (3) or (in the case the corresponding reaction lot is not, completing the computation) is found by respective steps.