A bill processing device capable of minimizing the possibility of entry of bills stored in a stacker into a bill transfer rout for obstructing the processing of a bill transferred next time, wherein a bill slip prevention means (9) for preventing the bill (101) in contact with a pair of guide parts (4) from slipping on the lateral thereof is disposed in the guide parts (4) allowing the bill (101) positioned on the pair of guide parts (4) into contact therewith among the bills (101) stored in the stacker (11), whereby the bills (101) stored in the stacker (11) can be prevented from entering the bill transfer route (3) by the bill slip prevention means.