An amending circuit includes a comparing unit, a predetermined voltage generating unit, a roller switch, alight emitting unit switch and a controlling unit. A pin of the mouse and the predetermined voltage generating unit are respectively connected to two input terminals of the comparing unit. The controlling unit is coupled to the light emitting unit switch and the roller switch. The controlling unit switches to a motion detecting mode to drive a current of the current source to flow toward a second pin via the first pin and a light emitting unit of the mouse. The controlling unit further switches to a roller detecting mode to set a pressure of the first pin lower than a predetermined voltage of the predetermined voltage generating unit while the roller is grounded or to set the first pin higher than the predetermined voltage while the roller is not grounded.