The present invention provides a display without using a composite oxide of cerium and a high oxygen storage capacity. One oxide of iron - zirconia composite oxide, wherein the iron containing zirconium and a rare earth element complex oxide, Fe2O3, oxides of ZrO2, and a rare earth element total content of less than 90% by mass, in terms of Fe2O3 iron oxide content of 10 to 90 mass%, after calcination in air over 5 hours to a temperature above 900 deg.] C using a composite oxide (1) to (3) :( the following formula wherein, Ii (Fe), ii (Zr) and ii (X) is a composite oxide by EPMA under predetermined conditions: a measurement point (the WDX wavelength dispersive X-ray spectroscopy) analysis determined by linear i (i = 1 ~ n) of iron, zirconium a rare earth element and X-ray intensity relative to 100% strength ratio of each element, Rav (Fe) and Rav (Zr + X) is the total measurement points Ri (Fe) and Ri (Zr + X) of the average value of n absolute values.) obtained covariance COV (Fe, Zr + X) is 20 or less. .