Shift-by-wire system

A shift-by-wire system that is mounted in a vehicle and actuates an object of actuation by driving a manual shaft on the basis of a shifting manipulation, comprising:

• an electric motor that includes a rotation shaft and rotates or drives the manual shaft by rotating or driving the rotation shaft;
• an angle-of-rotation sensor that detects an angle of rotation of the rotation shaft so as to control the electric motor;
• a shaft position sensor that detects the rotational position of the manual shaft;
• and
• a control unit that at an ordinary time at which the angle-of-rotation sensor functions normally, implements ordinary-time control to control the electric motor on the basis of the angle of rotation of the rotation shaft, which is sent from the angle-of-rotation sensor, so that the rotational position of the shaft sent from the shift position sensor will square with a target rotational position within a predetermined range, and that at an unordinary time at which the angle-of-rotation sensor does not normally function, implements unordinary-time control to initiate sensor-less control for controlling the electric motor while estimating the rotating direction of the rotation shaft of the electric motor on the basis of the rotational position of the shaft sent from the shift position sensor, and to cease the sensor-less control when the rotational position sent from the shift position sensor squares with the target rotational position within the predetermined range.