The invention relates to a step-by-step gearing mechanism, in particular for indexing a turret (12) on a machine tool, and having two cam plates (40, 40') which are each arranged about one axis (K, K') of rotation to be rotatably driven in the same direction and in relation to a roller carrier (30) in such a manner that circular holding regions (a, e) of both cam plates (40, 40') simultaneously rest on a roller (34) in each case to oppose each other, thereby preventing the roller carrier (30) from rotating. A projection (44, 44') of a cam plate (40, 40') subsequently rests on one roller (34) while another roller (34) dips into a cavity (c) of the other cam plate (40, 40') resulting in rotation of the roller carrier (30). The cam plates (40, 40') are adjacent each other and the projections (44, 44') thereof can be moved past each other to overlap with each other in such a manner that, to adapt to a change in said resting conditions, the holding regions (a, e) of both cam plates (40, 40') simultaneously rest on one and the same roller (34) to oppose each other, thereby in turn preventing rotation of the roller carrier (30). The projection (44, 44') of a cam plate (40, 40') subsequently rests on a roller (34), whereas the same roller (34) dips into the cavity (c) of the other cam plate (40', 40) resulting in the roller carrier (3) rotating again. The number of indexing positions in which the turret (12) can be held during each revolution is twice as large as the number of rollers (34) on the roller carrier (30).