PURPOSE: To ensure the simple and accurate calibration of a calorimeter for gas, by detecting the temperature rise only through the combustion improving gas for a temperature sensor of a gas calorimeter which detects the temperature during the oxidation reaction through an oxidation catalyst for the combustible gas which is diluted by a large quantity of the combustion improving gas (air etc.).

CONSTITUTION: A powder grain oxidation catalyst 2 is enclosed into a case 1 of a heat-resisting glass pipe, etc. Then the gas G diluted with a large quantity of the combustion improving gas like air, oxygen, etc. is supplied to the catalyst 2 from a branch pipe 3 via a temperature sensor 4. A calorimeter detects the temperature rise due to the oxidation by a temperature sensor 5. When the calibration is given to the calorimeter, only the combustion improving gas is made to pass and a heater 11 set around the sensor 5 of the catalyst 2 is heated with the conduction via a lead wire 10 piercing through a base 9 of a branch pipe of the case 1. In this case, the temperature rise is detected and the calibration is carried out from the prescribed calorific value required for heating and the output of detection of the sensor 5 and in response to the cooling conditions due to the combustion improving gas and equivalent to those required when the gas G is measured. In such a way, the calibration is possible easily without using the standard gas.