PURPOSE: To provide the correcting method and the correcting device of the machine parameter of a machine tool which can lead out the absolute value of the machine parameter intently.

CONSTITUTION: While a grinding wheel is made in a V-shaped grinding wheel having plural processing surfaces, plural first form generating surface data Dmi obtained by converting the input NC data Dsi by using a form generating model M is taken in a memory, and the first reference point Pr1 to correct the machine parameter q included in the first generating model M depending on the plural first form generating surface data Dmi is operated. And the actual grinding process surface of a work by the V-shaped grinding wheel is processed three-dimensionally to obtain plural second form generating data Ddi, the second reference point Pr2 to correct the machine parameter q included in the form generating model M depending on the plural second form generating surface data Ddi is operated, and the system is composed to correct the machine parameter q by comparing the first and the second reference points Pr1 and Pr2. Consequently, the absolute value of the machine parameter can be led out intently.