A speed sensor (10) fastened to a front folk (4) constituting a bicycle (1) with a cable tie (20) includes a sensor body (100) having a reed switch (110) detecting movement of a front wheel (2) in the bicycle (1), and a rubber pad (200) tied up on the front folk (4) and rotatably holding the sensor body (100) to vary a distance between the front wheel (2) and the reed switch (110).