To reduce recovery cost by bringing a used catalyst into contact with steam to vaporize molybdenum and sulfur components in the used catalyst and cooling the formed vapor to precipitate and recover molybdenum oxide and subsequently recovering the sulfur component as sulfate radicals.

When catalyst components are recovered from a used exhaust gas purifying catalyst, steam or steam-containing gas 1 is supplied to a catalyst packed tower 2 housing the used catalyst heated to 500-800°C to vaporize molybdenum and sulfur components in the used catalyst within the catalyst packed tower 2. The steam or steam-containing gas 1 containing both vaporized components is sent to a molybdenum recovery tower 3 to be cooled to temp. not becoming an acid dew point, and molybdenum oxide or molybdenic acid is precipitated to recover molybdenum from a molybdenum withdrawing system 7 before the sulfur component is recovered as sulfate radicals.