PURPOSE: To enable an accurate measurement of an optional point by finding a vonvertion coefficient corresponding the size measured with rotating in peripheral direction a cylindrical pellet of the standard nuclear fuel with the known size and by correcting the similar measuring value to the pellet of the material to be measured.

CONSTITUTION: A pellet P which is to be the standard or the material to be measured is placed on a base plate 14 and when phototubes 18, 19 detect it, a capstan roller 13 pushes the pellet P to free rollers 12a, 12b and the phototubes 18, 19 reconfirm the pellet P. The probe of digital dial gages 16, 17 is brought into contact with the outer peripheral face and the upper face and together with the rotation of the roller 13 at a fixed speed the pellet P is rotated as well. While the gage 16 is moved from the upper part to the lower part, then, the diameter and squareness of the outer peripheral face, the height and squareness of the upper face are measured, and the conversion coefficient is found by a microcomputer and also the measured value of the pellet P to be measured is corrected.