Abstract: To provide a calibration device for an apparatus filling a gas such as hydrogen gas and capable of precisely measuring quantity of the gas such as hydrogen gas that are filled at high pressure. A calibration device of the present invention is characterized by including a filling vessel, accommodated in a measurement housing, to the filling vessel a high pressure fuel gas such as hydrogen gas being fed from outside of the measurement housing, and a scale for measuring a weight of a fuel gas fed to the filling vessel, wherein a dry gas pipe for feeding a dry gas is detachably mounted in the measurement housing. Here, the scale preferably measures the weight of the fuel gas fed to the filling vessel together with a weight of the measurement housing.