1. A diagnosis assisting apparatus, comprising: volume data obtaining means, for obtaining a plurality of sets of volume data, each of which represent the state of a beating heart in different phases; coronary artery region extracting means, for extracting coronary artery regions from at least two sets of volume data from among the obtained sets of volume data; correlation establishing means, for setting a plurality of analysis points in each of the extracted coronary artery regions, and for establishing correlations among the analysis points, which are set at the same anatomical positions, within the plurality of coronary artery regions; index value calculating means, for calculating index values that indicate the character of plaque at each of the analysis points within all of the plurality of coronary artery regions; index value integrating means, for evaluating the character of plaque at positions within the coronary artery regions, by integrating the index values which are calculated at the plurality of analysis points corresponding to each of the positions; and output control means, for outputting the evaluation results regarding the character of plaque at each of the positions within the coronary artery regions, correlated with information regarding the positions.