When multiple kinds of bacterial colonies are present in a petri dish and, for example, a drug tolerance is to be measured, harvesting of mixed colonies of different types of bacteria makes it impossible to accurately determine the drug tolerance. Also, it is required to improve the throughput of a device for harvesting a bacterial colony. From images illuminated from multiple directions, isolating bacterial colonies are automatically extracted. Next, the image feature amounts are calculated from the multiple images that are illuminated from multiple directions and colonies are grouped depending on the feature amounts. Then, bacterial colonies to be harvested are determined based on the results of the grouping.