1. A traffic line creation device for creating a traffic line representing a motion trace of a tracking target, the device comprising: an object detector that detects the tracking target from a plurality of image frames to create a detected area of the tracking target in each of the plurality of image frames; a state determiner that determines a state of the tracking target based on the detected area in a current image frame and the detected area in an image frame at the time when the state of the tracking target was a normal state; a reference point creator that creates a single reference point of the tracking target for the detected area in each of the plurality of image frames, based on a process corresponding to the state determined by the state determiner; and a traffic line creator that creates a traffic line representing the motion trace of the tracking target by connecting the plurality of reference points created for the plurality of image frames.