To provide a paper sheet processing device which can check the fact that paper sheets discharged from a feed belt end in a paddle wheel stacking device are certainly imported between paddles, thereby preventing a stacking failure.

A stacking inlet sensor S1 and a paddle reference point sensor S2 for detecting stacked paper sheets are disposed. The paddle reference point sensor S2 detects paper sheets which pass through a portion of a paddle reference point TP1 at which a feed face formed by a feed belt 4 crosses the tips of paddle wheels 5a and 5b. The paddle wheels 5a and 5b are disposed on the same axle inside the two upper feed belts 4. The tips of paddles reach the paddle reference point TP1 at the timing when a paddle wheel rotary sensor S3 detects a paddle 5ap, and at that timing, the tips of paper sheets P1 pass through the nearest point Dmm of the paddle wheel reference point TP1, thereby stacking the paper sheets P1 between the paddles without fail.