Abstract: A motor driven flaring device in which a rotatable eccentric cone an apex of which defines a fixed center of rotation is pressed, while rotating, against an end of a pipe to be flared, including a body having a motor incorporated therein and having an output shaft to be connected to a drive source, a rotational drive shaft connected to the output shaft of the motor so as to relatively move in the axial direction thereof, a feed screw shaft member connected to the rotational drive shaft and screw-engaged by the body so as to rotate and move in the axial direction thereof, and a one-direction rotation transmission mechanism between the rotational drive shaft and feed screw shaft member for transmitting the rotation of the rotational drive shaft to the feed screw shaft member only in one direction.