An abdomen width determiner determines an abdomen width of a subject. A shape index calculator calculates a shape index corresponding to a cross-sectional shape of an abdomen of the subject. An obesity evaluator evaluates whether an obesity degree of the subject is high or low. An obesity index calculator calculates an obesity index corresponding to the abdomen width using a first equation if the obesity evaluator evaluates that the obesity degree is low, and calculates an obesity index corresponding to the abdomen width and the shape index using a second equation different from the first equation if the obesity evaluator evaluates that the obesity degree is high.
