PURPOSE: To carry out the working of grooving, etc. with a high degree of accuracy, in the working with use of a boundary between stacked articles as a reference, by moving a detecting head in the axial direction thereof to detect the boundary between the articles, and by moving a tool in accordance with the thus obtained positional data.

CONSTITUTION: When, for example grooving is carried out to a work which is formed by stacking a plurality of articles supported by a spindle bed 11 and a head stock 12, a control device 35 moves a detecting head H in the axial direction thereof to detect the boundary between the articles with the use of a change in eddy current due to the alternate magnetic field of a coil incorporated in the detecting head H, and computes the date of the boundary position in accordance with a signal from the detecting head H. Then, a tarret head 19 is rotated to make a tool T or a grinding wheel G face to the work W for setting the working position of the tool with the use of a boundary obtained from the date of the boundary position as a reference. Thus, the grooving or cutting-off to each article may be accurately and efficiently carried out.