Patent ID: 7279242

Claim:
A fuel cell system comprising: a fuel cell which generates electric power based on hydrogen and a oxidant gas supplied from the outside thereof; a hydrogen gas supply flow path for supplying the hydrogen to the fuel cell; a hydrogen off-gas circulating passage for returning hydrogen off-gas from said fuel cell to said hydrogen gas supply flow path; a hydrogen pump for boosting the hydrogen off-gas mounted in said hydrogen off-gas circulating passage; a hydrogen off-gas bypass passage which bypasses the hydrogen pump to return the hydrogen off-gas to said hydrogen gas supply flow path; and an ejector for sending the hydrogen off-gas in the hydrogen off-gas bypass passage to the hydrogen gas supply flow path, wherein a back flow check device is provided at said hydrogen off-gas bypass passage for checking back flow of the hydrogen off-gas, and wherein said back flow check device is an isolation valve, which is controlled in response to the driving state of said hydrogen pump.