Provided are a gas decomposing unit and an electrode for a fuel cell capable of stably supporting a gas decomposing catalyst. A gas decomposing unit and an electrode for a fuel cell each including: a carbon nanotube structure having a mesh structure in which functional groups bonded to plural carbon nanotubes are chemically bonded to mutually cross-link the plural carbon nanotubes; and a gas decomposing catalyst supported on the carbon nanotube structure. A method of manufacturing a gas decomposing unit characterized by including: an applying step of applying, to the surface of a substrate, a solution containing plural carbon nanotubes to which functional groups are bonded; a cross-linking step of chemically bonding the functional groups to build a mesh structure in which the plural carbon nanotubes mutually cross-link; and a supporting step of forming the carbon nanotube structure supporting a gas decomposing catalyst.