The present invention provides an indexing device for a turntable which is provided with a plurality of roller followers arranged at equal angular intervals; a cam component is provided on one side of the turntable. The cam component is provided with a first side rib wall with a continuous cam curved surface in a first direction and a second side rib wall with a continuous cam curved surface in a second direction, and the first side rib wall and the second side rib wall face opposite sides to form a cam groove with a variable groove width for guiding the movements of the roller followers and rotating the turntable; wherein the first side rib wall and the second side rib wall can compress on at least one pair of the roller followers of the turntable symmetrically in the first and second directions, so as to effectively eliminate the backlash problem between the cam component and the roller followers and improve the positioning accuracy of the turntable.