An attachment indexing apparatus which performs the steps of indicating an objective indexing position angle of an attachment by an indexing position angle indicating means 1, detecting the present position angle by a position detecting means 2, comparing the objective indexing position angle with the present position angle by an angle comparing means 3, determining the indexing rotation direction of the attachment by an indexing rotation direction determining means 4 in accordance with the compared result, calculating an indexing rotation angle of the attachment from the angle compared result and the indexing rotation direction by an indexing rotation angle calculating means 5, and indexing and rotating the attachment in accordance with the determined indexing rotation direction and the calculated indexing rotation angle.