A measurement unit (101) acquires a first value serving as a thermal conductivity index and a second value serving as a thermal diffusivity index, with respect to a fuel gas to be measured, at a first temperature, a second temperature, and a third temperature that are different from each other.
A change rate calculation unit (102) calculates a temperature change rate κ 1 of the first value between the first temperature and the second temperature, measured by the measurement unit (101), a temperature change rate κ 2 of the first value between the second temperature and the third temperature, a temperature change rate α 1 of the second value between the first temperature and the second temperature, and a temperature change rate α 2 of the second value between the second temperature and the third temperature. A calorific value calculation unit (103) calculates the calorific value of the fuel gas through a calorific value calculation formula in which the κ 1 , κ 2 , α 1 , and α 2 serve as explanatory variables and the calorific value serves as an object variable.