An objective of the present disclosure is to prevent paper sheets from being folded or damaged when the paper sheets are stacked. A paper sheet stacking mechanism (banknote stacking mechanism 50) includes stacking wheels 52, rotary rollers 54, a transport mechanism 70 configured to insert a paper sheet between vanes 52b of the stacking wheels, and a guide (center guide 55) having a guide surface 551 configured to guide the paper sheet. The guide surface has a curved shape having a diameter about a rotary shaft, and the diameter gradually increases from an upstream side toward a downstream side in a rotation direction of the stacking wheels.