A steering actuator of an independent type steer-by-wire system comprises a housing fixed to a vehicle body and an ultrasonic motor. The ultrasonic motor has a stator internally fixed to the housing and a rotator rotating relative to the stator when an electric current is applied. A steering rod having a first end and a second end penetrates through a center portion of the ultrasonic motor. The first end of the steering rod extends out of the housing for connection to a tie rod. In one embodiment, a ring gear, planetary gears, sun gear and/or racks formed at the steering rod are operably associated with converting rotating movement of the ultrasonic motor into linear movement of the steering rod. In another embodiment, a rotator ring, a plurality of pinions, worm gears and a plurality of racks formed at the steering rod are operably associated with converting rotating movement of the ultrasonic motor into linear movement of the steering rod.