To provide a gas filling device for a hydrogen fuel cell automobile, providing a desired hydrogen gas cooling effect even by the use of a simple heat exchanger.

The heat exchanger 10 is arranged in the middle of a gas pipe 7 connecting a gas tank 6 and a vehicle side receptacle 9 to which a dispenser side filling coupling is connected. The heat exchanger 10 is configured to have a plurality of branched pipes 11 branched from the gas pipe 7, a cooling fan 12, and fins 15. The channel cross sectional area of each branch pipe 11 in the heat exchanger 10 is formed larger than the channel cross sectional area of a gas pipe 7a on the upstream side of the heat exchanger. High-pressure hydrogen gas forcibly fed from a dispenser is throttled by a check valve in the receptacle 9 and adiabatically expanded, and also adiabatically expanded when led to flow into the branch pipe 11 to increase its temperature. However, the high-pressure hydrogen gas is emitted to the outside by cooling of the branch pipe 11 by the cooling fan 12. Therefore, in the gas tank 6, the temperature of hydrogen gas is mainly raised by adiabatic compression filling, and the temperature rise of the gas tank 6 is suppressed.