1. A cardiac function analysis apparatus comprising: a volume data storage means for storing a group of three-dimensional volume datasets that have been obtained by imaging the heart of a subject at predetermined time intervals; a position obtainment means for obtaining the positions of points in the heart that are present in at least two three-dimensional volume datasets in the group of three-dimensional volume datasets, the points anatomically corresponding to each other, and the at least two three-dimensional volume datasets having been obtained by imaging at different time from each other; a function information obtainment means for obtaining, based on each of the positions of the corresponding points in the heart, which have been obtained by the position obtainment means, three dimensional displacement vectors that represent displacements of the heart among the corresponding points as function information representing the function of the heart at each point within a three-dimensional space; and a display means for assigning colors that respectively represent the direction of the three dimensional displacement vectors to each point of the heart based on the function information, which has been obtained by the function information obtainment means, and displaying the colors assigned to each point at the positions of each of the points in an image that has the shape of the heart of the subject.