PURPOSE: To make it possible to index a cylindrical work provided with large and small windows without the work being damaged, by intermittently rotating the work, and by extending and retracting a locator having a wedge-like tip so that the indexing is made.

CONSTITUTION: A locator 67 having a wedge-like tip end is advanced by an air- cylinder 68 toward a work W formed, at unequal pitches, with small windows h1 through h4 and large windows H1, H2 and clamped on a clamper 51. When the locator 67 abuts against the outer peripheral wall surface of the work W or the taper part 67b of the locator 67 abuts against one of the small windows so that the rotation of the work W is stopped, air circuits are switched by dogs 71 through 74 corresponding to a rod 70 in accordnace with a change in the amount of the advance of the locator 67, and therefore, the locator 67 is once retracted. Then, the work W is rotated to a predetermined amount, and the locator 67 is again advanced. Therefore, the locator 67 finally abuts against one of the large windows H1, H2. The straight part 67a of the locator 67 is engaged with the large window H1, H2 of the work W which is rotated by the tapered part 67b, thereby the locating of the work W may be completed.