Abstract: A body fat combustion amount measurement device includes: a sample gas passage through which an exhaled gas flows; a sample gas chamber having an inlet through which a part of the exhaled gas flowing through the sample gas passage is introduced and an outlet through which the exhaled gas is discharged, the sample gas chamber configured to define an internal space through which the exhaled gas flows; a photoionization detector disposed in the internal space of the sample gas chamber and configured to generate an electrical signal corresponding to an amount of acetone contained in the exhaled gas existing inside the sample gas chamber; and a heater configured to increase a temperature of the internal space of the sample gas chamber to prevent moisture contained in the exhaled gas from being condensed in the sample gas chamber.