A personal authentication apparatus includes: an acquisition unit that acquires a measurement result including body weight and body impedance a calculation unit configured to, based on the measurement result acquired by the acquisition unit and personal information, calculate a calculation value relating to body composition that is less susceptible to temporal variation than body water amount a storage unit configured to store the body weight, the personal information, and the calculation value in association with measurement subject specification information that specifies the measurement subject a comparison unit configured to compare the most recent calculation value and a new calculation value and a measurement subject specification unit configured to, based on a difference between calculation values, specify which of the pieces of measurement subject specification information stored in the storage unit corresponds to the measurement result acquired by the acquisition unit.
