A mobile terminal comprising: a body comprising a first frame, and a second frame coupled to the first frame so as to be movable in a first direction with respect to the first frame; a roller rotatably coupled to the second frame; a flexible display unit divided, by being rolled around the roller, into a front portion located on a front surface of the body and a rear portion located on a rear surface of the body, and configured to output an image on one surface thereof; a support frame coupled to another surface of the flexible display unit and comprising a flexible rack gear formed on another surface of the support frame; and an auxiliary driving unit adapted to transfer a force to the flexible rack gear in a direction in which a size of an area of the flexible display unit that is located on the rear surface increases, wherein the auxiliary driving unit comprises: a pinion gear that is adapted to rotate by being meshed with the flexible rack gear; a motor, which is coupled to the second frame and is configured to provide rotational force to the pinion gear; wherein the pinion gear is configured to rotate in a first rotational direction when the second frame moves in the first direction; and wherein the motor is configured to: rotate the pinion gear in a second rotational direction, which is opposite the first rotational direction, when the second frame moves in a second direction; and rotate the pinion gear by a predetermined angle in the second rotational direction, which is opposite the first rotational direction, so as to provide tensile force to the flexible display unit in the first direction, when the second frame finishes moving in the first direction. a body comprising a first frame, and a second frame coupled to the first frame so as to be movable in a first direction with respect to the first frame; a roller rotatably coupled to the second frame; a flexible display unit divided, by being rolled around the roller, into a front portion located on a front surface of the body and a rear portion located on a rear surface of the body, and configured to output an image on one surface thereof; a support frame coupled to another surface of the flexible display unit and comprising a flexible rack gear formed on another surface of the support frame; and an auxiliary driving unit adapted to transfer a force to the flexible rack gear in a direction in which a size of an area of the flexible display unit that is located on the rear surface increases, wherein the auxiliary driving unit comprises: a pinion gear that is adapted to rotate by being meshed with the flexible rack gear; a motor, which is coupled to the second frame and is configured to provide rotational force to the pinion gear; wherein the pinion gear is configured to rotate in a first rotational direction when the second frame moves in the first direction; and wherein the motor is configured to: rotate the pinion gear in a second rotational direction, which is opposite the first rotational direction, when the second frame moves in a second direction; and rotate the pinion gear by a predetermined angle in the second rotational direction, which is opposite the first rotational direction, so as to provide tensile force to the flexible display unit in the first direction, when the second frame finishes moving in the first direction. a pinion gear that is adapted to rotate by being meshed with the flexible rack gear; a motor, which is coupled to the second frame and is configured to provide rotational force to the pinion gear; wherein the pinion gear is configured to rotate in a first rotational direction when the second frame moves in the first direction; and wherein the motor is configured to: rotate the pinion gear in a second rotational direction, which is opposite the first rotational direction, when the second frame moves in a second direction; and rotate the pinion gear by a predetermined angle in the second rotational direction, which is opposite the first rotational direction, so as to provide tensile force to the flexible display unit in the first direction, when the second frame finishes moving in the first direction. rotate the pinion gear in a second rotational direction, which is opposite the first rotational direction, when the second frame moves in a second direction; and rotate the pinion gear by a predetermined angle in the second rotational direction, which is opposite the first rotational direction, so as to provide tensile force to the flexible display unit in the first direction, when the second frame finishes moving in the first direction.