A servo includes a motor having a rotating shaft, an output shaft disposed apart from the rotating shaft, a transmission mechanism to transmit mechanical power from the motor to the output shaft, a circuit board, a first detected member fixed to an end of the rotating shaft, a second detected member fixed to an end of the output shaft adjacent to the circuit board; and a first detecting member and a second detecting member mounted on the circuit board and configured to respectively detect rotational angles of the rotating shaft and the output shaft, based on changes caused by rotation of the first detected member and the second detected member.