A sensor element comprising: a layered body that is formed by stacking a plurality of oxygen ion-conductive solid electrolyte layers, and that includes a measurement-object gas flowing portion (10-13, 20, 30, 40, 54, 61) formed therein to introduce measurement object gas from outside, the flowing direction of the measurement-object gas flowing portion (10-13, 20, 30, 40, 54, 61) being perpendicular to the stacking direction of the layered body; a measurement electrode mounting space that is a part of the measurement-object gas flowing portion, wherein the measurement electrode mounting space is partitioned from an inflow side of the measurement object gas by a partition wall, at least one diffusion rate-controlling portion that is a part of the measurement-object gas flowing portion, and that serves as a flow path through which the measurement object gas is introduced to the measurement electrode mounting space from the outside, the diffusion rate-controlling portion being formed as a slit between one or more and three or less surfaces of upper, lower, left and right inner peripheral surfaces of the measurement-object gas flowing portion and the partition wall, assuming a direction in which the solid electrolyte layers are stacked to be an up and down direction and a direction perpendicular to both the up and down direction and a direction in which the measurement object gas flows to be a right and left direction, and a measurement electrode that is formed in the measurement electrode mounting space at a position where the distance L between the measurement electrode and the exit of the diffusion rate-controlling portion is 0.1 mm or more, the surface of the measurement electrode being exposed to the measurement electrode mounting space; wherein the measurement electrode is either (a) formed on one of upper, lower, left and right inner peripheral surfaces of the measurement electrode mounting space, the one surface being different in direction from the surface along which the diffusion rate-controlling portion is formed; or (b) formed on a rear inner peripheral surface of the measurement electrode mounting space, the rear inner peripheral surface of the measurement electrode mounting space being oriented perpendicularly to the flowing direction of the measurement object gas and positioned on the downstream side in the flowing direction. a layered body that is formed by stacking a plurality of oxygen ion-conductive solid electrolyte layers, and that includes a measurement-object gas flowing portion (10-13, 20, 30, 40, 54, 61) formed therein to introduce measurement object gas from outside, the flowing direction of the measurement-object gas flowing portion (10-13, 20, 30, 40, 54, 61) being perpendicular to the stacking direction of the layered body; a measurement electrode mounting space that is a part of the measurement-object gas flowing portion, wherein the measurement electrode mounting space is partitioned from an inflow side of the measurement object gas by a partition wall, at least one diffusion rate-controlling portion that is a part of the measurement-object gas flowing portion, and that serves as a flow path through which the measurement object gas is introduced to the measurement electrode mounting space from the outside, the diffusion rate-controlling portion being formed as a slit between one or more and three or less surfaces of upper, lower, left and right inner peripheral surfaces of the measurement-object gas flowing portion and the partition wall, assuming a direction in which the solid electrolyte layers are stacked to be an up and down direction and a direction perpendicular to both the up and down direction and a direction in which the measurement object gas flows to be a right and left direction, and a measurement electrode that is formed in the measurement electrode mounting space at a position where the distance L between the measurement electrode and the exit of the diffusion rate-controlling portion is 0.1 mm or more, the surface of the measurement electrode being exposed to the measurement electrode mounting space; wherein the measurement electrode is either (a) formed on one of upper, lower, left and right inner peripheral surfaces of the measurement electrode mounting space, the one surface being different in direction from the surface along which the diffusion rate-controlling portion is formed; or (b) formed on a rear inner peripheral surface of the measurement electrode mounting space, the rear inner peripheral surface of the measurement electrode mounting space being oriented perpendicularly to the flowing direction of the measurement object gas and positioned on the downstream side in the flowing direction. (a) formed on one of upper, lower, left and right inner peripheral surfaces of the measurement electrode mounting space, the one surface being different in direction from the surface along which the diffusion rate-controlling portion is formed; or (b) formed on a rear inner peripheral surface of the measurement electrode mounting space, the rear inner peripheral surface of the measurement electrode mounting space being oriented perpendicularly to the flowing direction of the measurement object gas and positioned on the downstream side in the flowing direction.