The invention provides a catalyst for carbon monoxide conversion, comprising from 10 to 90% by mass of a copper oxide ingredient, from 5 to 50% by mass of a zinc oxide ingredient and from 10 to 50% by mass of an aluminum oxide ingredient, and having a specific surface area of from 100 to 300 m2/g, a carbon monoxide adsorption of from 20 to 80 μmol/g, and a copper oxide crystallite diameter of at most 200 angstroms, as a catalyst suitable for carbon monoxide conversion for fully reducing carbon monoxide in the hydrogen gas obtained through reforming of a starting hydrocarbon material, for the purpose of enabling stable long-term operation of a fuel cell which uses hydrogen gas as a fuel and which is frequently and repeatedly started and stopped.