An image processing apparatus comprising: a storage unit which is adapted to take in a plurality of slice images acquired from a specific area of a specimen by Z-stack shootings performed at different time points, to associate the plurality of slice images each with a shooting time point and a slice height z at the shooting time point, and to store the plurality of slice images as one of several slice image groups created successively in the same manner; a manual selecting unit which is adapted to allow a user to manually select a slice image from one of the slice image groups stored by the storage unit as a representing slice image of said one of the slice image groups; and an automatic selecting unit which is adapted to automatically select a slice image from another one of the slice image groups stored by the storage unit, as a representing slice image of said another one of the slice image groups, based on selecting standard information indicating a result of the manual selection, wherein the selecting standard information includes stack coordinates (t, z) which indicate the shooting time point t and the slice height z of the manually selected slice image, characterized in that the number of said one of slice image groups is equal to or larger than two, and given the stack coordinates (t 1, z 1), (t 2, z 2),... of two or more slice images manually selected from two or larger number of said one of slice image groups, the stack coordinates (t', z') of the automatically selected slice image are located near a curve defined by the manually selected coordinates (t 1, z 1), (t 2, z 2),... on the t-z plane. a storage unit which is adapted to take in a plurality of slice images acquired from a specific area of a specimen by Z-stack shootings performed at different time points, to associate the plurality of slice images each with a shooting time point and a slice height z at the shooting time point, and to store the plurality of slice images as one of several slice image groups created successively in the same manner; a manual selecting unit which is adapted to allow a user to manually select a slice image from one of the slice image groups stored by the storage unit as a representing slice image of said one of the slice image groups; and an automatic selecting unit which is adapted to automatically select a slice image from another one of the slice image groups stored by the storage unit, as a representing slice image of said another one of the slice image groups, based on selecting standard information indicating a result of the manual selection, wherein the selecting standard information includes stack coordinates (t, z) which indicate the shooting time point t and the slice height z of the manually selected slice image, characterized in that the number of said one of slice image groups is equal to or larger than two, and given the stack coordinates (t 1, z 1), (t 2, z 2),... of two or more slice images manually selected from two or larger number of said one of slice image groups, the stack coordinates (t', z') of the automatically selected slice image are located near a curve defined by the manually selected coordinates (t 1, z 1), (t 2, z 2),... on the t-z plane.