A sheet feeder includes a roller, a reflector, a sensor, and a rotating speed detector. The reflector is integrally attached to the roller, the reflector including first reflecting surfaces and second reflecting surfaces arranged alternately along a circumference direction of the roller. The sensor includes a light emitter and a light receiver. The rotating speed detector is configured to detect a rotating speed of the roller based on a result of the detection by the sensor. Each of the first reflecting surfaces reflects the inspection light at a first reflection ratio, and provides a first reflection light path along which the inspection light is directed to the light receiver. Each of the second reflecting surfaces reflects the inspection light at a second reflection ratio smaller than the first reflection ratio, and provides a second reflection light path along which the inspection light is directed outside the light receiver.