A power transmission device comprising: a motor configured to drive a rotary shaft; a first reducer connected to the rotary shaft and configured to reduce rotational angular velocity of the rotary shaft; a second reducer connected to the rotary shaft and configured to reduce rotational angular velocity of the rotary shaft; a first clutch disposed between the rotary shaft and the first reducer and configured to connect and disconnect the rotary shaft and the first reducer; and a second clutch disposed between the rotary shaft and the second reducer and configured to connect and disconnect the rotary shaft and the second reducer; wherein the second reducer comprises: a second sun gear disposed on one side of the second clutch and configured to be engaged with the rotary shaft or disengaged from the rotary shaft by the second clutch; and a second planetary gear disposed on the outside of the second sun gear and engaged with the second sun gear, wherein the second reducer further comprises a ring gear disposed on the outside of the second planetary gear and engaged with the second planetary gear, characterized by a third clutch disposed outside the second reducer and configured to connect and disconnect the second reducer and an external component, wherein the third clutch is configured to connect and disconnect the ring gear and the external component; and by a fourth clutch configured to connect and disconnect the second reducer and the external component, wherein the fourth clutch is configured to connect and disconnect the second sun gear and the external component. a motor configured to drive a rotary shaft; a first reducer connected to the rotary shaft and configured to reduce rotational angular velocity of the rotary shaft; a second reducer connected to the rotary shaft and configured to reduce rotational angular velocity of the rotary shaft; a first clutch disposed between the rotary shaft and the first reducer and configured to connect and disconnect the rotary shaft and the first reducer; and a second clutch disposed between the rotary shaft and the second reducer and configured to connect and disconnect the rotary shaft and the second reducer; wherein the second reducer comprises: a second sun gear disposed on one side of the second clutch and configured to be engaged with the rotary shaft or disengaged from the rotary shaft by the second clutch; and a second planetary gear disposed on the outside of the second sun gear and engaged with the second sun gear, wherein the second reducer further comprises a ring gear disposed on the outside of the second planetary gear and engaged with the second planetary gear, characterized by a third clutch disposed outside the second reducer and configured to connect and disconnect the second reducer and an external component, wherein the third clutch is configured to connect and disconnect the ring gear and the external component; and by a fourth clutch configured to connect and disconnect the second reducer and the external component, wherein the fourth clutch is configured to connect and disconnect the second sun gear and the external component. a second sun gear disposed on one side of the second clutch and configured to be engaged with the rotary shaft or disengaged from the rotary shaft by the second clutch; and a second planetary gear disposed on the outside of the second sun gear and engaged with the second sun gear, wherein the second reducer further comprises a ring gear disposed on the outside of the second planetary gear and engaged with the second planetary gear, characterized by a third clutch disposed outside the second reducer and configured to connect and disconnect the second reducer and an external component, wherein the third clutch is configured to connect and disconnect the ring gear and the external component; and by a fourth clutch configured to connect and disconnect the second reducer and the external component, wherein the fourth clutch is configured to connect and disconnect the second sun gear and the external component.