A composite oxide powder including a composition formula (1), wherein the ratio α/β of a surface area value α(m2/g) calculated by a BET one-point method to a surface area value β(m2/g) calculated from a formula (2) is greater than 1.0 and equal to or less than 1.5 and the surface area value α is equal to or less than 20 m2/g. ABO3-δ (1) (wherein A is one or more types of elements (La, Sr, Sm, Ca and Ba), B is one or more types of elements (Fe, Co, Ni and Mn) and 0≤δ