PURPOSE: To inspect the wear of each cutting tool by measuring both of the reference diametric dimension of the outer circumferential surface of a master provided for a lathe and a diametric dimension of each test piece by each bite every cutting position, determining the difference between the aforesaid reference diametric dimension and each measured diametric dimension, and thereby comparing each difference with an allowable limit.

CONSTITUTION: In a CPU 21, the reference diametric dimension d0 which is inputted by a data inputting device 24 and stored in a memory device 23, is subtracted from respective measured diametric dimensions d1, d2,... at a subtracted from respective measured diametric dimensions X1, X2,... are thereby computed. If a cutting tool Ta does not wear, its difference X shall be zero, and the computed value which is two times as much as the abrasion loss of the bite Ta, shall be its difference X. The difference Xi=di-d0 is inputted into a comparison section 21c every each cutting tool Ta1, Ta2,..., and is compared with a correction area value XHL which is inputted by the data inputting device 24 while being stored in the memory section 23, so as to be inspected whether or not the wear of each cutting tool is within an allowable limit.