A compensating mechanism includes a base, an adjusting unit, an adjusting cover and a stop unit. The adjusting unit is disposed in the base. The adjusting cover connects to the adjusting unit and includes a curved groove. The stop unit is disposed between the adjusting unit and the base and includes a pin. When the adjusting cover is rotated, the adjusting unit is only rotated with respect to the base and the stop unit is axially moved with respect to the base so that the pin enters or leaves the curved groove.