1. A method of measuring the density of a plurality of defects that occur in a single crystal for each type of defect, characterized by comprising: etching an observation surface, which is a surface of the single crystal, to form an etch pit at each defect; calculating the maximum depth, mean depth and depth curvature of each of etch pits formed at a plurality of defects present within a predetermined area on the observation surface; and comparing the measured maximum depth, mean depth and depth curvature with respective reference values to determine the type of each defect within the predetermined area.