A CPR image that represents a range corresponding to at least a portion of a blood vessel is generated from volume data obtained by imaging, and arranged in a predetermined region of a display screen. Band shaped condition display regions are arranged outside the predetermined region such that they are parallel to the blood vessel represented by the CPR image. Index values, such as stenosis rates and whether plaque is present, are calculated by analyzing the volume data. The calculated index values are converted to colors (RGB values) by referring to a conversion table. The condition display regions are displayed in colors according to the values of the index values.