To quantify the aggregation ability of various types of blood cells respectively within a short period of time. An apparatus for achieving the above-described object, which includes: a TV camera for taking an image of blood flow; an image processing section for identifying the types of blood cells contained in a blood cell retention part, in which blood cells are retained, from a blood flow image taken by the TV camera; and an aggregation ability calculation device for calculating at least one of the area, cell count and position of blood cells of each type as the aggregation ability of blood.