A method for identifying a colony, in which an undifferentiated colony, an undefined colony, a differentiated colony and a multi-layered colony are identified based on a taken image inside of an incubator of multipotent stem cells, the method comprising obtaining a circularity C of the colony by calculation, determining the luminance B of the colony, and identifying the colony as an undifferentiated colony, an undefined colony or a differentiated colony based on the luminance B of the colony in the taken image, in addition to the circularity C; wherein, when a predetermined first threshold of a circularity of the colony is C1 and a second threshold of the circularity of the colony is C2 (C1 < C2), the circularity C of the colony is obtained by calculation, and a colony satisfying C 2 ≦ C is determined as the undifferentiated colony containing only undifferentiated multipotent stem cells, and a colony satisfying C 1 ≦ C < C 2 is determined as an undefined colony that is potentially the undifferentiated colony, and wherein it is further determined that a colony satisfying C < C 1 is the differentiated colony containing multipotent stem cells; and wherein, when the undifferentiated colony that is identified based on the circularity C is, the undefined colony that is identified based on the circularity C is, the differentiated colony that is identified based on the circularity C is, a first predetermined threshold for the luminance of the colony in a taken image is B1, a second predetermined threshold for the luminance of the colony is B2, a third predetermined threshold for the luminance of the colony is B3, and a fourth predetermined threshold for the luminance of the colony is B4 (B1 < B2 < B3 < B4), a colony satisfying B2 ≦ B ≦ B3 for all luminances within a colony contour is determined as an undifferentiated colony (a), a colony satisfying B < B1 for some of the luminances within the colony contour is determined as a multi-layered colony (d), a colony satisfying B4 < B for some of the luminances within the colony contour is determined as a differentiated colony (c), and a colony other than the undifferentiated colony (a), the multi-layered colony (d) and the differentiated colony (c) is determined as an undefined colony (b), then a colony satisfying and (a) is determined as the undifferentiated colony, a colony satisfying and (b), or satisfying and (a), or satisfying and (b) is determined as the undefined colony, a colony satisfying (d) is determined as the multi-layered colony containing multipotent stem cells that are stacked to form multiple layers, and a colony satisfying (c), or satisfying and (a), or satisfying and (b) is determined as the differentiated colony. a colony satisfying and (a) is determined as the undifferentiated colony, and (a) is determined as the undifferentiated colony, a colony satisfying and (b), or satisfying and (a), or satisfying and (b) is determined as the undefined colony, and (b), or satisfying and (a), or satisfying and (b) is determined as the undefined colony, a colony satisfying (d) is determined as the multi-layered colony containing multipotent stem cells that are stacked to form multiple layers, and (d) is determined as the multi-layered colony containing multipotent stem cells that are stacked to form multiple layers, and a colony satisfying (c), or satisfying and (a), or satisfying and (b) is determined as the differentiated colony. (c), or satisfying and (a), or satisfying and (b) is determined as the differentiated colony.