A sensor element 101 includes an element main body 101a that includes oxygen ion-conductive solid electrolyte layers (1 to 6), and a porous protective layer 90 that covers at least part of the element main body 101a. The porous protective layer 90 includes a porous inner protective layer 92 and a porous outer protective layer 91 disposed on the outer side of the inner protective layer 92 and having a smaller average pore diameter than the inner protective layer 92.