The equipment which measures a diameter of small and deep hole whose aspect ratio is about 80 has been developed. The light projected to a specimen makes a small spot in a small hole. The position of wall in a hole is recognized by detecting an image of small spot reflected at the wall. Taking a ferrule (the hole diameter=125.0-126.0μm, the length=10mm) which is used for optical connector as a specimen, the hole diameter at a height of 5 mm from the end is measured using this equipment. The measured diameters are in the region of 125.8-126.1μm. The true value of diameters are in the region of 125.9-126.0μm. Therefore, the measuring errors are within ±0.2μm.