1. An image processing apparatus comprising: a storage unit which takes in a plurality of slice images acquired from a specific area of a specimen by each of Z-stack shootings performed at different time point, associates the plurality of slice images each with a shooting time point and a slice height z of the shooting time point, and stores the plurality of slice images as one of slice image groups; a manual selecting unit which allows a user to manually select a slice image from one of slice image groups stored by the storage unit as a representing slice image of said one of slice image groups; and an automatic selecting unit which automatically selects a slice image from another one of slice image groups stored by the storage unit, as a representing slice image of said another one of slice image groups, based on a selecting standard information indicating a result of the manual selection.