PURPOSE: To correctly measure the diameter, length and shape change of a grindstone by arranging a contact detecting means detecting the contact of a grindstone, a main shaft indexing means indexing the grindstone at optional angle and an arithmetic means operating the dimension of the grindstone from the position detected by the contact detecting means.
CONSTITUTION: In case of measuring the diameter and length of a grindstone T, the grindstone T is fitted to a main shaft 1 and moved toward a contact detecting means 6. The moving amt. of the grindstone is calculated by an arithmetic means 8 by the contact of the grindstone T with this contact detecting means 6. This calculated value is then subtracted from the reference distance between a preknown main shaft origin and the contact detecting means 6 by the arithmetic means 8 to find the dimension of the grindstone T. As a result, the diameter, length and shape change of the grindstone T can correctly be measured without accompanying any interference with the probe of the contact detecting means 6 and any wear of the probe.