A pseudo defect sample for adjusting an ultrasonic flaw detection measurement condition to inspect a defect within a target material, the pseudo defect sample comprising a substrate which has a first surface and a second surface opposed to the first surface, the substrate having a counterbore which is formed therein from a side of the first surface to a first depth, and a flat-bottomed hole which is formed from the bottom surface of the counterbore to a second depth and formed in a part of a bottom surface of the counterbore, and a ratio ϕ/d of an equivalent circle diameter ϕ of the flat-bottomed hole to the second depth d of the flat-bottomed hole being: 0.08 or more and less than 0.40 when the equivalent circle diameter ϕ of the flat-bottomed hole is less than 0.3 mm; 0.1 or more and less than 0.60 when the equivalent circle diameter ϕ of the flat-bottomed hole is 0.3 mm or more and less than 0.4 mm; and 0.11 or more and less than 1.60 when the equivalent circle diameter ϕ of the flat-bottomed hole is 0.4 mm or more.