A gas sensor including a conductive oxide sintered body, the sintered body including a crystal phase having a perovskite-type oxide crystal structure represented by a compositional formula : REaCubFecNidOx wherein RE represents a rare earth element, wherein the following conditions : a+b+c+d=1 and 1.25≦x≦1.75 are satisfied, and wherein a, b, c, and d satisfy the following conditions : 0.375≦a≦0.524; 0.050
