A sheet stopping mechanism includes a guiding element, a sheet stopping element and a guiding slot. The guiding element includes a sheathing part and an extension arm. The sheathing part is sheathed around an axle of the sheet pick-up roller. The sheet stopping element includes a stopping part, a protrusion part and a contact part. The extension arm of the guiding element is upwardly sustained against at the contact part of the sheet stopping element. The protrusion part of the sheet stopping element is accommodated within the guiding slot. When the sheet pick-up roller is moved toward a sheet input tray, the guiding element is uplifted. As a result, the protrusion part of the sheet stopping element is shifted and rotated in the guiding slot, and a front edge of the paper sheet is no longer hindered by the stopping part of the sheet stopping element.