NOVELTY - A substance shut-off device for shutting down communication of an inflammable substance and/or an oxidizer, comprises a shut-off mechanism, which operates by heat generated accompanying a reaction between the inflammable substance and the oxidizer in a catalyst (101) portion, to shut down communication of inflammable substance and/or oxidizer.    USE - The substance shut-off device is for shutting down communication of an inflammable substance (comprising hydrogen) and/or an oxidizer (comprising oxygen), when the inflammable substance and oxidizer are brought into contact with each other, preventing continuation of the contact between the inflammable substance and the oxidizer. It is useful for a fuel cell (claimed).    ADVANTAGE - The substance shut-off device has simple structure, and is driven without use of drive energy, such as electricity to shut down communication of an inflammable substance or oxidizer.    DETAILED DESCRIPTION - A substance shut-off device for shutting down communication of an inflammable substance and/or an oxidizer, when the inflammable substance and oxidizer are brought into contact with each other, preventing continuation of the contact between the inflammable substance and the oxidizer, comprises a catalyst portion provided in an inflammable substance flow path (102) or an oxidizer flow path; and a shut-off mechanism, which operates by heat generated accompanying a reaction between the inflammable substance and the oxidizer in the catalyst portion, to shut down communication of inflammable substance and/or oxidizer.    An INDEPENDENT CLAIM is also included for a fuel cell, comprising a cell portion comprising a fuel electrode for being supplied with a fuel, an oxidizer electrode for being supplied with an oxidizer, and an ionic conductor between the fuel electrode and the oxidizer electrode; a fuel flow path; an oxidizer flow path; a detection mechanism, which generates heat by contact between the oxidizer and fuel; and a shut-off mechanism provided in the fuel flow path and/or oxidizer flow path, and thermally coupled to the detection mechanism, for shutting down communication of the fuel and/or oxidizer based on the heat generation of the detection mechanism.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view showing a substance shut-off device.    Catalyst (101)    Flow path (102)    Gas flow (103)    Material (111)