The present invention provides a method and device capable of measuring body fat accurately in a simple manner and at a low cost. The method comprises a measuring process (ST200) where a distribution of skin surface temperature of the subject is measured a first operation process (ST210) where temperature gradient on the skin surface is evaluated from the measured skin temperature a second operation process (ST230) where a skin temperature distribution is calculated by conducting a numerical heat conduction analysis on a prearranged sample body composition with the temperature gradient imposed as the boundary condition a comparing process (ST240) where the skin temperature distributions obtained in the measuring and second operation processes are compared and a modification process (ST260) where the body composition of the sample is modified if the two skin temperature distributions disagree in the comparing process. The second operation and modification processes are executed repeatedly until the two skin temperature distributions become sufficiently close.
