Abstract: A paper-stopping mechanism applied in an automatic document feeder (ADF). The paper-stopping mechanism includes a shaft, a stepping motor for carrying the shaft to rotate, a cam structure having a first protruding portion and a second protruding portion and carried by the shaft to rotate the first protruding portion and the second protruding portion thereof, a paper-stopping arm having a bearing point, wherein the bearing point is moved against by the first protruding portion to move the paper-stopping arm upward, and an elastic buckling device for buckling the paper-stopping arm when the paper-stopping arm is moving upward to stay at a paper-feeding position, and for shifting when the second protruding portion of the cam structure is rotated against the elastic buckling device for removing the paper-stopping arm from the elastic buckling device to return to a paper-stopping position.