To enhance the accumulation efficiency with a simple structure.

This sheet sorting device comprises a sorter part 28 provided under a discharge port 27a for sensitive materials 20a. The sorter part 28 comprises a frame 31, a carrying belt 32a, a flapper 33a, a guide member 34a, and a stopper 35. The flapper 33a is displaceable between a receiving position and a delivering position. Further, it is obliquely raised in the receiving position to receive photosensitive materials 20a. The flapper is laid in a horizontal state in the delivering position to deliver accumulated photosensitive materials 45a and 45b to the carrying belt 32a. The photosensitive materials 20a of the same order are fallen in a batch onto the flapper 33a. After the flapper 33a is displaced to the delivering position, the carrying belt 32a is fed by a prescribed quantity to partially overlap the following accumulated photosensitive materials 45b to the accumulated photosensitive materials of the previous order, for example, 45a.