Abstract: An object of the present invention is to provide a living body measuring device which, once the personal information having been set therein, executes an arithmetic operation simply by making a measurement without requiring a user to remember his/her personal memory number. The living body measuring device of the present invention stores the measured body weight value and/or bioelectrical impedance value as well as the personal body information set in the initial stage, compares the measured values with those stored values, and determines a current subject who is being measured by considering the most proximal values to be the data associated with the measured subject, thereby calculating a body-related index automatically. Especially, if both of the bioelectrical impedance and the body weight are used, then the determination may be more accurate.