PURPOSE: To measure the accurate calorie of combustible gas, by calculating the difference between the temperature measured before oxidation and that measured after oxidation after setting a temperature sensor, a powder grain oxidation catalyst and a temperature sensor successively to a flow path of the combustible gas diluted with a large quantity of the combustion improving gas.

CONSTITUTION: A gas inlet end pipe 2 and a waste gas outlet end pipe 3 are stuck to both ends of a case 1 of a round pipe made of heatresisting glass, etc. A powder grain oxidation catalyst 4 of Cu2O, etc. is packed to a center part of the case 1, and branch pipes 5 and 6 are fitted into both sides of the catalyst 4 to set temperature sensors 9 and 10 which are supported by lead wires 8 through bases 7. The glass-wool 11 is packed around the sensors 9 and 10. Then the gas G obtained by diluting the combustible gas by 200W2,000 times with the combustion improving gas such as air, O2, etc. is supplied through the pipe 2. A temperature t0 of the sensor 9 and a temperature t1 of the sensor obtained after the oxidation are measured, and then the calorific value Q of the gas G is obtained with the calculation shown in an equation and from the specific heat at constant pressure Cp of the combustion improving gas. In such a way, the calorific value can be measured accurately in a continuous and instantaneous way with a simple constitution.