The present invention provides a method for constructing cell lineage that is less labor intensive and requires less time as a result of using a computer. The method comprises the step for obtaining a plurality of 2D images different in focal plane and a time by taking a plurality of the 2D images by changing the focal plane and taking a plurality of the 2D images in a time series for a cell constituting the subject of observation. The method further comprises the steps of extracting a nucleus area by carrying out image processing for individual 2D images; unifying the nucleus area, which is derived from the identical nucleus, from the nucleus area extracted from the individual 2D images; and constructing the cell lineage from a time and a position, where the nucleus area appears and disappears in the image, in the unified nucleus area.