A pressure loss in an oxidative gas passage of each of single cells is obtained This pressure loss is compared with predetermined ranks so as to carry out classification according to the ranks. The pressure loss in the oxidative gas passage has a predetermined permissible range comprising a first rank, a second rank , . . . , and an n-th rank respectively. The single cell that is to be measured at the moment is classified into a certain one of the ranks depending on which one of the first to n-th ranks corresponds to the pressure loss in the oxidative gas passage. Classification is similarly carried out as to a pressure loss in a fuel gas passage as well. Those of the single cells which are equivalent in rank are gathered up and combined to fabricate a fuel cell.