PURPOSE: To obtain an indexing head whose structure is simple and action is reliable, by a method wherein an indexing gear whose diameter is large is fixed to an indexing table, an indexing position is detected by an indexing switch and the indexing position is corrected by operations of a positioning piece and a positioning shaft.

CONSTITUTION: An indexing gear 3 having a large diameter is provided on the back of an indexing table 4 and the gear 3 is supported rotatably on a main spindle 2 secured on a machine bed by a bearing 10, in a device wherein a replacement head fixing frame 6 is installed on the circumference of the indexing table 4 ascendably and descendably. Dogs 11... are fixed on the bottom face of the gear 3 and the dog 11 is detected by a detecting switch 12 so as to stop a motor 13. A positioning tool 15 having a protruded part on one side of the tool 15 is provided on a pinion shaft 14a to be revolved by the motor 13 and an indexing is decided accurately by pinching and holding a roller 15a provided on the edge of the protruded part of the positioning tool 15 which is in the vicinity of a normal position when the pinion is revolved by positioning shafts to be advanced from both sides.