To provide a combustion heat quantity measuring system, using a cone calorimeter capable of stable measurements.

The outside air is supplied toward the cone calorimeter 1 by an indoor air suction part 2. In the cone calorimeter 1, combustion of a sample is performed similarly as hitherto fore. Combustion gas, generated by combustion, is discharged outside through an outdoor exhaust part 3. Since the outside air is sent into the cone calorimeter 1 in this system, even if condition fluctuation of the indoor air occurs, stable combustion heat quantity measurement can be performed, without being influenced by the fluctuations in the condition. Hereby, accuracy of acquired measurement data is improved.