A sensor element comprising: a multilayer structure including a plurality of oxygen-ion-conductive solid-electrolyte layers (1, 2, 3, 4, 5, 6) that are stacked one on top of another, and a measurement-object-gas-flowing portion provided in the multilayer structure and from one end of which a measurement-object gas is introduced into the multilayer structure; a measuring electrode exposed in a space in which the measuring-electrode is set and which is part of the measurement-object-gas-flowing portion; an outer electrode provided on an outer surface of the multilayer structure; and a blocking portion including at least one of an inner blocking layer and an outer blocking layer, the inner blocking layer covering at least part of an exposed portion where the solid-electrolyte layers (1, 2, 3, 4, 5, 6) are exposed as inner surfaces of the space in which the measuring-electrode is set, the inner blocking layer not conducting one or more kinds of substances that contain oxygen, the outer blocking layer being provided in a portion of the multilayer structure that is exposed to the measurement-object gas and covering at least part of a nearest portion that is at a shortest distance from the space in which the measuring-electrode is set among portions of outer surfaces of the multilayer structure where the solid-electrolyte layers (1, 2, 3, 4, 5, 6) are exposed, the outer blocking layer not conducting one or more kinds of substances that contain oxygen wherein the blocking portion has a porosity of 5% or lower; and wherein the blocking portion is made of at least one selected from alumina, silica, mullite, silicon nitride and silicon carbide. a multilayer structure including a plurality of oxygen-ion-conductive solid-electrolyte layers (1, 2, 3, 4, 5, 6) that are stacked one on top of another, and a measurement-object-gas-flowing portion provided in the multilayer structure and from one end of which a measurement-object gas is introduced into the multilayer structure; a measuring electrode exposed in a space in which the measuring-electrode is set and which is part of the measurement-object-gas-flowing portion; an outer electrode provided on an outer surface of the multilayer structure; and a blocking portion including at least one of an inner blocking layer and an outer blocking layer, the inner blocking layer covering at least part of an exposed portion where the solid-electrolyte layers (1, 2, 3, 4, 5, 6) are exposed as inner surfaces of the space in which the measuring-electrode is set, the inner blocking layer not conducting one or more kinds of substances that contain oxygen, the outer blocking layer being provided in a portion of the multilayer structure that is exposed to the measurement-object gas and covering at least part of a nearest portion that is at a shortest distance from the space in which the measuring-electrode is set among portions of outer surfaces of the multilayer structure where the solid-electrolyte layers (1, 2, 3, 4, 5, 6) are exposed, the outer blocking layer not conducting one or more kinds of substances that contain oxygen wherein the blocking portion has a porosity of 5% or lower; and wherein the blocking portion is made of at least one selected from alumina, silica, mullite, silicon nitride and silicon carbide.