To provide a calibration device for apparatus filling a gas such as hydrogen gas and capable of precisely measuring quantity of the gas that is filled at high pressure. A calibration device of the present invention includes: a filling vessel 2, accommodated in a measurement housing 1, to the filling vessel 2 a high pressure fuel gas such as hydrogen gas being fed from outside of the measurement housing 1; a scale 3 for measuring a weight of a fuel gas fed to the filling vessel 2; and a control device CU for eliminating an error caused by changing buoyant force from a gas in the measurement housing before and after filling the fuel gas.