1. A human tracking apparatus comprising: a storing unit which stores an inputted frame image; a detecting unit which detects persons photographed in the inputted frame image; a registering unit which registers already detected persons, photographed in at least one previous inputted frame image, as candidates, wherein the at least one previous inputted frame image is associated with the inputted frame image; a calculating unit which calculates indices indicating the similarity between the persons detected in the inputted frame image and the candidates based on two or more parameters in relation to all combinations of the persons and the candidates; a normalizing unit which normalizes the calculated indices indicating the similarity; an integrating unit which integrates the normalized indices indicating the similarity for each combination of the persons detected in the inputted frame image and the candidates; and a tracking unit which identifies at least one of the persons being the same as at least one of the candidates based on the integrated indices indicating the similarity.