A planetary differential reduction device for synchronously rotating and differentially rotating a first output shaft and a second output shaft, characterized in comprising: a first sun gear of a fixed side; a second sun gear having a same number of teeth as the first sun gear and disposed adjacent to the first sun gear in a direction of a device axis; a first planetary gear meshed with the first sun gear; a second planetary gear having a same number of teeth as the first planetary gear and meshed with the second sun gear; a common planetary carrier for supporting the first planetary gear and the second planetary gear; a first internal gear meshed with the first planetary gear; and, a second internal gear meshed with the second planetary gear and having a same number of teeth as the first internal gear, wherein the first internal gear is connected to a side of the first output shaft, the second internal gear is connected to a side of the second output shaft, and the second sun gear is an input element for inputting a rotation for differentially rotating the second output shaft with respect to the first output shaft; the planetary differential reduction device further comprises: a planetary reduction part connecting the second internal gear and the second output shaft, wherein the planetary reduction part comprises: a third sun gear integrally rotating with the second internal gear; a third planetary gear meshed with the third sun gear; a third internal gear meshed with the third planetary gear; and, a planetary carrier for supporting the third planetary gear, and wherein the planetary carrier is connected to the second output shaft, characterized by the third internal gear rotating integrally with the first internal gear. a first sun gear of a fixed side; a second sun gear having a same number of teeth as the first sun gear and disposed adjacent to the first sun gear in a direction of a device axis; a first planetary gear meshed with the first sun gear; a second planetary gear having a same number of teeth as the first planetary gear and meshed with the second sun gear; a common planetary carrier for supporting the first planetary gear and the second planetary gear; a first internal gear meshed with the first planetary gear; and, a second internal gear meshed with the second planetary gear and having a same number of teeth as the first internal gear, wherein the first internal gear is connected to a side of the first output shaft, the second internal gear is connected to a side of the second output shaft, and the second sun gear is an input element for inputting a rotation for differentially rotating the second output shaft with respect to the first output shaft; the planetary differential reduction device further comprises: a planetary reduction part connecting the second internal gear and the second output shaft, wherein the planetary reduction part comprises: a third sun gear integrally rotating with the second internal gear; a third planetary gear meshed with the third sun gear; a third internal gear meshed with the third planetary gear; and, a planetary carrier for supporting the third planetary gear, and wherein the planetary carrier is connected to the second output shaft, characterized by the third internal gear rotating integrally with the first internal gear. a planetary reduction part connecting the second internal gear and the second output shaft, wherein the planetary reduction part comprises: a third sun gear integrally rotating with the second internal gear; a third planetary gear meshed with the third sun gear; a third internal gear meshed with the third planetary gear; and, a planetary carrier for supporting the third planetary gear, and wherein a third sun gear integrally rotating with the second internal gear; a third planetary gear meshed with the third sun gear; a third internal gear meshed with the third planetary gear; and, a planetary carrier for supporting the third planetary gear, and wherein the planetary carrier is connected to the second output shaft, characterized by the third internal gear rotating integrally with the first internal gear.