To stabilize a characteristic of a diffusion limiting current, so as to stabilize a sensor output and to enhance detection precision.

This sensor is provided with the first gas diffusion layer 2 for make a measured gas diffuse in an inside, an oxygen ion-conductive solid electrolyte layer 5, and an inside electrode 3 provided between the first gas diffusion layer 2 and the solid electrolyte layer 5 to be introduced with the measured gas through the first gas diffusion layer 2, and for making the diffusion limiting current flow to an outside electrode provided outside the solid electrolyte layer 5. The second gas diffusion layer 4 is formed to be arranged between the first gas diffusion layer 2 and a gaseous atmosphere of the measured gas.