To provide a gas compressor which utilizes an advantage of using a Stirling engine as a driving source, camprising a buffer space.

A compressor 10 is driven by a Stirling engine 2 which involves a buffer space 3. Gas 4 sucked from outside and compressed by a compressor 10 is introduced to a buffer space 3 through a compressed gas introduction passage 11 branched from a compressed gas supply passage 17. As a result, buffer pressure in the buffer space 3 increases automatically, therefore, it is possible to eliminate a troublesome processing such as charging high-pressure gas into the buffer space 3 from the outside. The high-pressure gas 4 can be supplied into the buffer space 3 all the time, therefore, it is possible to avoid such an aging decrease in internal pressure in a buffer space as found in a conventional type, dispensing with maintenance. Further, the buffer space 3 can be used as a receiver tank (gas accumulating chamber).