To provide a limit current type oxygen sensor for diagnosing the presence or absence of deterioration when using a sensor, judging that the deteriorating occurred if any deterioration should be detected, and preventing erroneous use.

One cathode electrode film 2 is formed at one surface side of a sheet-shaped oxygen ion conductive solid electrolyte 1 and an anode auxiliary electrode film 3a and an anode main electrode film 3b are formed on the other surface side. The area of the anode main electrode film 3b is equal to or more than 60% and equal to or less than 90% of the total area of an anode electrode film and the total area is within ±10% of the area of the cathode electrode film 2. Then, a diffusion limiting body 5 with an oxygen diffusion hole 4 for communicating with the cathode electrode film 2 inside is arranged on it. A current Ib flowing through the anode main electrode film 3b and a current Iab flowing through the anode electrode films 3a and 3b is read, thus judging that a sensor deteriorated (no limit current characteristics) when the current ratio Ib/Iab is larger than a setting value which is stored in advance.