Where a DNA chip corresponding to a bacterium that is a subsequently added identification object is produced, temporal and pecuniary cost is reduced, and even where a probe unique to the DNA sequence of an identification object cannot be designed, precision in identifying DNA comprised in a sample is maximized. First, on designing a probe, a plurality of different probes are prepared to one kind of bacterium. Where some probes come to be not available by addition of bacteria that are new identification objects, identification is carried out using the remaining probes. Where a probe unique to an identification target bacterium cannot be designed, a probability of correct identification is increased by using multiple probes. Moreover, in consideration with a possibility that multiple kinds of bacteria simultaneously exist, a combination of probes that maximizes a probability of correct identification is selected.