To obtain an inexpensive and small stacker mechanism whose configuration is simple.

The mechanism includes a guide plate 7 provided so as to be drooped from an exhaust port of a medium processing device, an accumulating plate 8 disposed so as to be inclined by a first angle to the guide plate and for rotating with a supporting point 9 provided at an end as a center, and a locking means 11 provided at a lower side of the accumulating plate 8, for locking the accumulating plate 8 at a changed second angle when the accumulating plate is made to be rotated downwardly and its inclination angle is changed to the second angle, and for releasing locking by further depressing the accumulating plate 8, wherein the inclination angle of the accumulating plate 8 is changed in response to the accumulating amount of tickets A which are ejected from the exhaust port and accumulated on the accumulating plate 8.