NOVELTY - Reactor comprises a reaction member comprising an electrolyte portion containing solid electrolyte, a fuel electrode portion arranged integrally with the electrolyte portion and contacting a fuel gas to react the fuel gas; and other than the reaction member, an electrically conductive member made of metal containing iron and chromium which is electrically connected with the air electrode portion to give and receive electrical power to and from the air electrode portion.    USE - The reactor is useful for industrial applications.    ADVANTAGE - The invention suppresses the oxidization of the surface, i.e. the formation of chromia on the surface, while maintaining the electrical conductivity of the electrically conductive member made of iron-series metal containing chromium (e.g. stainless steel).    DETAILED DESCRIPTION - Reactor comprises a reaction member comprising an electrolyte portion containing solid electrolyte, a fuel electrode portion arranged integrally with the electrolyte portion and contacting a fuel gas to react the fuel gas, and an air electrode portion arranged integrally with the electrolyte portion and contacting an oxygen-containing gas to react the oxygen-containing gas; and other than the reaction member, an electrically conductive member made of metal containing iron and chromium which is electrically connected with the air electrode portion to give and receive electrical power to and from the air electrode portion, where metal film is formed on the surface of at least the portion on the electrically conductive member, which is electrically connected with the air electrode portion; and a first heat-treatment is performed on the electrically conductive member after the formation of the metal film, in a state in which an ambient pressure is adjusted to a negative pressure lower than an atmospheric pressure; and the electrically conductive member and the air electrode portion are electrically connected by electrically connecting the air electrode portion and a post-heat-treatment metal film surface, which is the surface of the portion on which the metal film is formed and then the first heat-treatment is performed; or reactor comprises a reaction member comprising an electrolyte portion containing solid electrolyte, a fuel electrode portion arranged integrally with the electrolyte portion and contacting a fuel gas to react the fuel gas, and an air electrode portion arranged integrally with the electrolyte portion and contacting an oxygen-containing gas to react the oxygen-containing gas; and other than the reaction member, an electrically conductive member made of metal containing iron and chromium which is electrically connected with the air electrode portion to give and receive electrical power to and from the air electrode portion, where the air electrode portion and the electrically conductive member are electrically connected through the metal film; a layer containing chromium oxide (Cr2O3) is formed at the boundary between the electrically conductive member and the metal film; and the thickness of the layer containing Cr2O3 is 0.8 mu m or less. An INDEPENDENT CLAIM is a producing method of a reactor, which comprises a reaction member comprising an electrolyte portion containing solid electrolyte, a fuel electrode portion arranged integrally with the electrolyte portion and contacting a fuel gas to react the fuel gas, and an air electrode portion arranged integrally with the electrolyte portion and contacting an oxygen-containing gas to react the oxygen-containing gas; and other than the reaction member, an electrically conductive member made of metal containing iron and chromium which is electrically connected with the air electrode portion to give and receive electrical power to and from the air electrode portion, where the method comprises a metal film forming step for forming metal film on the surface of at least the portion on the electrically conductive member, which is electrically connected with the air electrode portion, a first heat-treatment step for performing a first heat-treatment on the electrically conductive member after the metal film forming step, in a state in which an ambient pressure is adjusted to a negative pressure lower than an atmospheric pressure; and an electrically connecting step for electrically connecting the electrically conductive member and the air electrode portion by electrically connecting the air electrode portion and a post-heat-treatment metal film surface, which is the surface of the portion with the metal film formed to it, after the first heat-treatment step.