A locking device configured to fix and lock an object having an empty space defined therein, wherein the device comprises: a fixing assembly configured to pivot via a load of an object to fix the object; and a locking assembly configured to control a locked or unlocked state of the fixing assembly via a user input operation, wherein the locking assembly includes a locking insert, wherein the fixing assembly comprises: first and second spaced-apart brackets; first and second pivoting portions pivotally coupled to the first and second brackets respectively; first and second pivoting-driving portions integrally formed to lower ends of the first and second pivoting portions respectively, wherein when the first and second pivoting-driving portions are pivoted downwardly via a load of the object, the first and second pivoting portions are pivotally moved such that upper ends thereof are closer to each other, wherein the first and second pivoting-driving portions have first and second insert-receiving portions integrally formed to the first and second pivoting-driving portions respectively at lower ends thereof, wherein the first and second insert-receiving portions have first and second through-holes defined therein respectively, wherein when the first and second pivoting-driving portions are fully pivoted downwardly, the locking insert horizontally passes through the first and second through-holes; and first and second position-fixing portions extending inwardly from the upper ends of the first and second pivoting portions respectively, wherein when the first and second pivoting portions are fully pivotally moved such that upper ends thereof are fully close to each other, the first and second position-fixing portions are inserted into the empty spaced defined in the object, thereby to fix a position of the object, wherein when the locking insert horizontally passes through the first and second through-holes, the fixing assembly is in a locked state. a fixing assembly configured to pivot via a load of an object to fix the object; and a locking assembly configured to control a locked or unlocked state of the fixing assembly via a user input operation, wherein the locking assembly includes a locking insert, wherein the fixing assembly comprises: first and second spaced-apart brackets; first and second pivoting portions pivotally coupled to the first and second brackets respectively; first and second pivoting-driving portions integrally formed to lower ends of the first and second pivoting portions respectively, wherein when the first and second pivoting-driving portions are pivoted downwardly via a load of the object, the first and second pivoting portions are pivotally moved such that upper ends thereof are closer to each other, wherein the first and second pivoting-driving portions have first and second insert-receiving portions integrally formed to the first and second pivoting-driving portions respectively at lower ends thereof, wherein the first and second insert-receiving portions have first and second through-holes defined therein respectively, wherein when the first and second pivoting-driving portions are fully pivoted downwardly, the locking insert horizontally passes through the first and second through-holes; and first and second position-fixing portions extending inwardly from the upper ends of the first and second pivoting portions respectively, wherein when the first and second pivoting portions are fully pivotally moved such that upper ends thereof are fully close to each other, the first and second position-fixing portions are inserted into the empty spaced defined in the object, thereby to fix a position of the object, first and second spaced-apart brackets; first and second pivoting portions pivotally coupled to the first and second brackets respectively; first and second pivoting-driving portions integrally formed to lower ends of the first and second pivoting portions respectively, wherein when the first and second pivoting-driving portions are pivoted downwardly via a load of the object, the first and second pivoting portions are pivotally moved such that upper ends thereof are closer to each other, wherein the first and second pivoting-driving portions have first and second insert-receiving portions integrally formed to the first and second pivoting-driving portions respectively at lower ends thereof, wherein the first and second insert-receiving portions have first and second through-holes defined therein respectively, wherein when the first and second pivoting-driving portions are fully pivoted downwardly, the locking insert horizontally passes through the first and second through-holes; and first and second position-fixing portions extending inwardly from the upper ends of the first and second pivoting portions respectively, wherein when the first and second pivoting portions are fully pivotally moved such that upper ends thereof are fully close to each other, the first and second position-fixing portions are inserted into the empty spaced defined in the object, thereby to fix a position of the object, wherein when the locking insert horizontally passes through the first and second through-holes, the fixing assembly is in a locked state.