A hardness tester for determining the hardness of a sample by measuring a size of an impression formed on a surface of the sample, placed on a sample stage, by impressing an indenter with predetermined test load, comprising: an image capture control means for obtaining image data of the surface of the sample by controlling an image capture means and making the image capture means capture an image of the surface; an impression region extracting means for extracting an impression region formed on the surface of the sample based on the image data obtained by the image capture control means; an impression vertex extracting means for extracting a vertex for measuring the impression to measure a size of the impression based on the impression region extracted by the impression region extracting means; and a hardness calculating means for calculating hardness of the sample based on the vertexes for measuring the impression extracted by the impression vertex extracting means; characterized in that: the impression region extracting means binarizes the image data of the surface of the sample, applies a reduction processing and an expansion processing to the binarized image data, applies a distance conversion processing to the reduction/expansion processed image data, and extracts a closed region corresponding to a contour of the indenter by using the distance-converted image data, and the impression vertex extracting means estimates the vertex for measuring the impression based on a profile of the closed region extracted by the impression region extracting means, and extracts a point in the binarized image data, as the vertex for measuring the impression, that agrees with a predetermined condition based on the estimated vertex. an image capture control means for obtaining image data of the surface of the sample by controlling an image capture means and making the image capture means capture an image of the surface; an impression region extracting means for extracting an impression region formed on the surface of the sample based on the image data obtained by the image capture control means; an impression vertex extracting means for extracting a vertex for measuring the impression to measure a size of the impression based on the impression region extracted by the impression region extracting means; and a hardness calculating means for calculating hardness of the sample based on the vertexes for measuring the impression extracted by the impression vertex extracting means; characterized in that: the impression region extracting means binarizes the image data of the surface of the sample, applies a reduction processing and an expansion processing to the binarized image data, applies a distance conversion processing to the reduction/expansion processed image data, and extracts a closed region corresponding to a contour of the indenter by using the distance-converted image data, and the impression vertex extracting means estimates the vertex for measuring the impression based on a profile of the closed region extracted by the impression region extracting means, and extracts a point in the binarized image data, as the vertex for measuring the impression, that agrees with a predetermined condition based on the estimated vertex. the impression region extracting means binarizes the image data of the surface of the sample, applies a reduction processing and an expansion processing to the binarized image data, applies a distance conversion processing to the reduction/expansion processed image data, and extracts a closed region corresponding to a contour of the indenter by using the distance-converted image data, and the impression vertex extracting means estimates the vertex for measuring the impression based on a profile of the closed region extracted by the impression region extracting means, and extracts a point in the binarized image data, as the vertex for measuring the impression, that agrees with a predetermined condition based on the estimated vertex.