A gas supply device for use in a fuel cell system, comprises: a first injector configured to have a first maximum valve-openable pressure; a second injector arranged in parallel with the first injector and configured to have a lower flow rate than the first injector and a greater second maximum valve-openable pressure than the first maximum valve-openable pressure; a first pressure sensor located upstream of the first and second injectors; and a controller configured to control open/close operation of the first and second injectors, wherein at a start of the fuel cell system, (i) when pressure in the upstream of the first and second injectors is greater than the first maximum valve-openable pressure but is less than or equal to the second maximum valve-openable pressure, the controller opens the second injector, and (ii) when the pressure in the upstream of the first and second injectors is less than or equal to the first maximum valve-openable pressure, the controller opens the first injector or the second injector.