To increase the temperature of a detection unit efficiently and reduce the power consumption efficiently.SOLUTION: A gas sensor element 100 includes: an element body 400 having an oxygen concentration detection cell 130 and an oxygen pump cell 140; and a protective layer 20 covering the element body 400. The element body 400 is a heat generator which generates heat by conduction, and contains a heater 200 for heating the oxygen concentration detection cell 130 and the oxygen pump cell 140. A protective layer 20 includes a first protective layer 21 formed in such a manner that a carrier mainly composed of a white ceramic supports a noble metal catalyst and a second protective layer 22 mainly composed of a white ceramic, in which a noble metal catalyst is not supported. The second protective layer 22 covers the outer surface of the first protective layer 21, has the surface serving as the outermost surface of the protective layer 20, and has a larger thickness than the first protective layer 21.SELECTED DRAWING: Figure 4
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