Abstract: A concentration measurement apparatus includes a sample temperature sensor, optical sensors, an environmental temperature sensor, a storage unit storing second correlation information between first difference information between the environmental temperature and a temperature of a calibration sample, and second difference information between a theoretical temperature based on first correlation information between the temperature and a transmittance of the calibration sample with respect to a measurement value of the transmittance of the calibration sample measured by the concentration measurement apparatus 1 and the measurement value of the temperature of the calibration sample.