1. A diagnosis assisting apparatus, characterized by comprising: blood vessel extracting means, for extracting a blood vessel region that represents a blood vessel from volume data obtained by imaging, and for setting a core of the blood vessel and a plurality of cross sections perpendicular to the core; CPR image generating means, for generating a CPR image that represents a range corresponding to at least a portion of the blood vessel based on data regarding the blood vessel region, the core, and each of the cross sections; condition estimating means, for estimating the condition of stenosis of the blood vessels at each of the cross sections, by analyzing data included in the blood vessel region at each of the cross sections, and the condition of stenosis is represented by index values; color determining means, for determining each color corresponding to each index value that represents the estimated condition of stenosis in each of the cross sections; and display control means, for arranging the CPR image in a predetermined region of a display screen, arranging at least one band shaped condition display region parallel to the center line of the blood vessel represented by the CPR image, and for displaying the condition display region with colors in which each color determined by the color determining means is plotted at the position thereof corresponding to each portion of the cross sections in the CPR image.