A probe unit comprising: a plurality of large diameter probes, each of which is formed by using conductive material, is extendable in a longitudinal direction and has an axisymmetric shape; a plurality of small diameter probes, each of which is formed by using conductive material, has a diameter smaller than a diameter of each large diameter probe and has an axisymmetric shape; a large-diameter probe holder that includes a plurality of large hole portions which are configured to individually hold the plurality of large diameter probes; and a plurality of reception hole portions, each of which has a diameter smaller than a diameter of each large hole portion, communicates with any one of the plurality of large hole portions, and configured to receive an end portion of the small diameter probe so that the end portion comes into contact with the large diameter probe, wherein each set of one of the large hole portions and corresponding one of the reception hole portions that communicate with each other pierces through the large-diameter probe holder in a thickness direction; and a small-diameter probe holder that includes a plurality of small hole portions which are configured to individually hold the plurality of small diameter probes while preventing the small diameter probes from coming off and which pierce through the small-diameter probe holder, and that is configured to be stacked on the large-diameter probe holder so that each of the small hole portions communicates with any one of the plurality of reception hole portions, wherein central axes in the longitudinal direction of the large hole portion and the small hole portion that communicate with each other are separated from each other, and the plurality of small hole portions include two small hole portions which are adjacent to each other and of which central axes in the longitudinal direction are separated from each other by a distance shorter than a distance between central axes in the longitudinal direction of two large hole portions that are corresponding to the two small hole portions. a plurality of large diameter probes, each of which is formed by using conductive material, is extendable in a longitudinal direction and has an axisymmetric shape; a plurality of small diameter probes, each of which is formed by using conductive material, has a diameter smaller than a diameter of each large diameter probe and has an axisymmetric shape; a large-diameter probe holder that includes a plurality of large hole portions which are configured to individually hold the plurality of large diameter probes; and a plurality of reception hole portions, each of which has a diameter smaller than a diameter of each large hole portion, communicates with any one of the plurality of large hole portions, and configured to receive an end portion of the small diameter probe so that the end portion comes into contact with the large diameter probe, wherein each set of one of the large hole portions and corresponding one of the reception hole portions that communicate with each other pierces through the large-diameter probe holder in a thickness direction; and a small-diameter probe holder that includes a plurality of small hole portions which are configured to individually hold the plurality of small diameter probes while preventing the small diameter probes from coming off and which pierce through the small-diameter probe holder, and that is configured to be stacked on the large-diameter probe holder so that each of the small hole portions communicates with any one of the plurality of reception hole portions, wherein central axes in the longitudinal direction of the large hole portion and the small hole portion that communicate with each other are separated from each other, and the plurality of small hole portions include two small hole portions which are adjacent to each other and of which central axes in the longitudinal direction are separated from each other by a distance shorter than a distance between central axes in the longitudinal direction of two large hole portions that are corresponding to the two small hole portions.