The device pertains to instrumentation technology and can be used in energy production, metallurgy, chemical industry to determine hydrogen concentration in fluid and gas media in a wide range of temperatures and pressures. The hydrogen detector for gas and fluid media comprises a selective membrane and a housing with a potential measuring unit inside, a ceramic sensing element made of solid electrolyte with a standard electrode in its cavity, a porous platinum electrode applied to the external layer of the ceramic sensing element, a sealed lead-in tightly fixed inside the housing above the ceramic sensing element, the potential measuring unit that passes through the center hole of the sealed lead-in and the lower bushing. The ceramic sensing element is designed as the cylindrical element interlinked with the bottom, located in the lower part of the cylinder. The external cylindrical surface of the ceramic sensing element is tightly connected to the inner side surface of the housing. The standard electrode is located in the inner cavity of the ceramic sensing element. The external part of the ceramic sensing element bottom is covered with a layer of porous platinum electrode. The end of the potential measuring unit central core is brought out to the standard electrode. The lower bushing designed as a tube is connected to the lower part of the housing from the side of the ceramic sensing element. The lower end of the lower bushing has a bottom with a center hole with the selective membrane attached. The lower free end of the selective membrane is tightly closed with a plug; the cavity limited by the inner surface of the lower bushing, the external part of the bottom of the ceramic sensing element and the inner surfaces of the selective membrane and the plug is leak-tight. The detector is additionally provided with an upper bushing and glass-ceramic sealant. The technical result is the enhanced service life and reliability of the hydrogen detector operation in a wide range of working medium parameters by providing leak-tightness of the inner cavity of the ceramic sensing element. 4 dependent claims, 1 figure.