A probe unit includes: large diameter probes; small diameter probes; a large-diameter probe holder having large hole portions which individually hold the large diameter probes, and reception hole portions which have diameters smaller than those of the large hole portions, communicate with the large hole portions, and receive end portions of the small diameter probes so that the end portions come into contact with the large diameter; and a small-diameter probe holder probes having small hole portions which individually hold the small diameter probes. The central axes of the large hole portion and the small hole portion that communicate with each other are separated from each other, and the small hole portions include two small hole portions which are adjacent to each other and of which central axes are separated from each other by a distance shorter than a distance between the central axes of two large hole portions that are corresponding to the two small hole portions.