There are provided an image acquiring unit (122) for acquiring a plurality of images of a skin of an examination subject which is picked up over a plurality of points of time by an image pickup device (104), a body hair specifying unit (123) for specifying body hair for a growth period of the examination subject from the image with regard to each of the images acquired by the image acquiring unit (122), and a circadian rhythm estimating unit 124 for estimating a circadian rhythm of the examination subject based on a temporal change in a length of the body hair for the growth period which is obtained by specifying the body hair for the growth period from each of the images by the body hair specifying unit 123. Consequently, it is possible to estimate the circadian rhythm of the examination subject from these images by simply acquiring the image of the skin of the examination subject without requiring gene measurement, cell culture, frequent blood collection, analysis in special research facilities or the like.
