A sensor element includes an element main body having an oxygen ion-conducting solid electrolyte body, a detection electrode which is disposed on an outer surface of the element main body and contains Pt and Au, a reference electrode which is disposed in the element main body, a connecting terminal for detection electrode which is disposed on the outside of the element main body, a lead portion for detection electrode which contains Pt, is disposed on the outside of the element main body, and electrically connects between the detection electrode and the connecting terminal for detection electrode, a lower insulating layer which is disposed between the lead portion for detection electrode and the element main body and insulates the two from each other, and an upper insulating layer which covers a surface of the lead portion for detection electrode and has a porosity of 10% or less.