To provide a gas filling device capable of preventing gas from flowing to the drive device side even if the gas leaks from a compressor.

A partition wall 15 dividing the inside of a housing 2 into an engine room 13 and a compressor room 14 is provided in the housing 2 for storing an engine 3 and a compressor 4 therein. The engine 3 is disposed in the engine room 13, and the compressor 4 is disposed in the compressor room 14. A communication hole 19 communicating the engine room 13 with the compressor room 14 is formed in the partition wall 15. The crankshaft 33 of the engine 3 is inserted into the communication hole 19. An air outlet 21 is formed in the compressor room 14. A main air discharge fan 23 of compressor drive type is provided for discharging the air inside the compressor room 14 from the air outlet 21. An air inlet 18 is formed in the engine room 13.