A servo includes a housing including a gear shaft supporting and positioning structure therein, an electric motor arranged within the housing, a speed reduction gear set, an output gear shaft including a front end protruding out of the housing and a rear end located within the housing, an angle detection device, and a control circuit board. The electric motor is engaged with the output gear shaft through the speed reduction gear set. The rear end of the output gear shaft is connected to the angle detection device. The control circuit board is connected to the electric motor and the angle detection device. The angle detection device includes a magnetic sensor arranged on the control circuit board and a magnet that is connected to the rear end of the output gear shaft and located right in front of the magnetic sensor.