PURPOSE: To remove AsH3, PH3, B2H6 and SeH2 with good efficiency, by molding a composition prepared by compounding copper oxide with either one of silicon oxide, aluminum oxide and zinc oxide in a specific compounding ratio to use the molded body adjusted to specific density.

CONSTITUTION: Alkali is added to lead nitrate and zinc nitrate to form a precipi tate which is, in turn, baked to be converted to oxide or a silica gel or alumina sol is mixed with a cupric oxide powder and the resulting mixture is kneaded and dried to obtain a composition. In this case, the constitutional components are compounded so as to adjust a metal atomic ratio M/(M+Cu) (wherein M is Si, Al or Zn) to 0.02W0.7. This composition is molded into a pellet form to obtain a molded body with density of 1.5W3.5g/ml. This molded body is packed as a purifying agent and contacted with gas containing harmful compo nents exhausted from a semiconductor manufacturing process to remove AsH3, PH3, B2H6 and SeH2 being harmful components.