There is provided a substance shutoff device for shutting down the communication of at least one of an inflammable substance and an oxidizer when the inflammable substance and the oxidizer are brought into contact with each other to thereby prevent further contact between the inflammable substance and the oxidizer. The substance shutoff device comprises a catalyst portion provided in contact with one of an inflammable substance flow path and an oxidizer flow path; and a shutoff means, which operates by heating through a reaction between the inflammable substance and the oxidizer in the catalyst portion to shut down the communication of at least one of the inflammable substance and the oxidizer. A fuel cell using the inflammable substance shutoff device is also provided.