PURPOSE: To obtain the element which is superior in sensitivity and selectivity, is particularly linear in resistance value change for isobutane gas density and is large in gas density separating characteristic by providing a catalyst layer containing specific Bi2O3-MoO3 on the surface of the sensitive body containing specific amounts of ZnO, Me2O and Me2'O3 (where Me is one of Li, Na, K, Rb and Me' of Ga, B, In, Fe, Al, Cr).