Body moisture meter comprising a sensor unit (121) which is configured to output a signal relating to the amount of moisture inside a living body by being in contact with a body surface of an armpit of a subject, a conversion means which is configured to convert the signal from the sensor unit to the amount of body water, a display means (112) which is configured to display the amount of body water obtained by the conversion means and a changing means which is configured to changs the display mode by the display means so as to call users attention in a case in which the amount of body water obtained by the conversion means is lower than a first reference value, whereinthe first reference value is a value corresponding to a predetermined value between 25% to 40%. Calibration of the moisture meter is done measuring the moisture in the air and in water and associating the values 0% and 100%, respectively.
