Disclosed is a monitoring method for visualizing a location of an inactive livestock in a livestock pen. This method includes extracting, by a video analysis device, livestock objects from a video image acquired for each frame and subsequently calculating center coordinates indicating a location of the inactive livestock based on coordinates of the extracted livestock objects, displaying, by a display device, an object icon representing the inactive livestock in a display region mapped to the calculated center coordinate among a plurality of display regions defined on a display screen, and emitting light by light emitting units selected based on the calculated center coordinate, among a plurality of lighting units installed in a livestock structure.