An industrial robot, comprising: a base portion; an arm unit provided to the base portion; and an arm drive unit for driving the arm unit; wherein the arm unit has a lower arm mechanism including a parallel link structure, and an upper arm mechanism provided to a top portion of the lower arm mechanism, wherein the lower arm mechanism has a front link including a lower end rotatably connected to the base portion and a rear link including a lower end rotatably connected to the base portion, wherein the arm drive unit has a lower arm drive mechanism for driving the lower arm mechanism, wherein the lower arm drive mechanism has a lower ball screw including a nut and a shaft, and a lower bearing portion supporting the shaft so as to be rotatable about its axis, wherein an extending portion extending from the lower end (8A, 9A) of either one of the front link and the rear link is connected to the nut so as to be rotatable about a nut side rotational axis, wherein the lower bearing portion is connected to the base portion so as to be rotatable about a bearing portion side rotational axis, wherein the nut side rotational axis and the bearing portion side rotational axis are parallel with rotational axes of the front link and the rear link, wherein the lower arm mechanism has a lateral link including both ends rotatably connected to an upper end of the front link and an upper end of the rear link, respectively, and wherein the upper arm mechanism is connected to the lateral link so as to be rotatable about an upper arm rotational axis, characterized in that the arm drive unit has an upper arm drive mechanism for driving the upper arm mechanism, the upper arm drive mechanism has an upper ball screw including a nut and a shaft, and an upper bearing portion supporting the shaft of the upper ball screw so as to be rotatable about its axis, the upper arm mechanism is connected to the nut of the upper ball screw at a position different from the upper arm rotational axis so as to be rotatable about a nut side rotational axis, wherein the upper bearing portion is connected to the lateral link so as to be rotatable about a bearing portion side rotational axis, and wherein the nut side rotational axis and the bearing portion side rotational axis of the upper ball screw are parallel with the upper arm rotational axis. a base portion; an arm unit provided to the base portion; and an arm drive unit for driving the arm unit; wherein the arm unit has a lower arm mechanism including a parallel link structure, and an upper arm mechanism provided to a top portion of the lower arm mechanism, wherein the lower arm mechanism has a front link including a lower end rotatably connected to the base portion and a rear link including a lower end rotatably connected to the base portion, wherein the arm drive unit has a lower arm drive mechanism for driving the lower arm mechanism, wherein the lower arm drive mechanism has a lower ball screw including a nut and a shaft, and a lower bearing portion supporting the shaft so as to be rotatable about its axis, wherein an extending portion extending from the lower end (8A, 9A) of either one of the front link and the rear link is connected to the nut so as to be rotatable about a nut side rotational axis, wherein the lower bearing portion is connected to the base portion so as to be rotatable about a bearing portion side rotational axis, wherein the nut side rotational axis and the bearing portion side rotational axis are parallel with rotational axes of the front link and the rear link, wherein the lower arm mechanism has a lateral link including both ends rotatably connected to an upper end of the front link and an upper end of the rear link, respectively, and wherein the upper arm mechanism is connected to the lateral link so as to be rotatable about an upper arm rotational axis, characterized in that the arm drive unit has an upper arm drive mechanism for driving the upper arm mechanism, the upper arm drive mechanism has an upper ball screw including a nut and a shaft, and an upper bearing portion supporting the shaft of the upper ball screw so as to be rotatable about its axis, the upper arm mechanism is connected to the nut of the upper ball screw at a position different from the upper arm rotational axis so as to be rotatable about a nut side rotational axis, wherein the upper bearing portion is connected to the lateral link so as to be rotatable about a bearing portion side rotational axis, and wherein the nut side rotational axis and the bearing portion side rotational axis of the upper ball screw are parallel with the upper arm rotational axis.