NOVELTY - Manufacture of catalyst (LL) involves forming liquid including ultrapure water (GG), reducing agent, and an electrode catalyst precursor using chlorine-species-containing material, forming liquid (HH) by adding ultrapure water to obtained liquid, filtrate-washing the catalyst precursor in liquid (HH) using ultrapure water, preparing liquid (KK) in which the catalyst precursor is dispersed in the liquid as for which below the setting value (V1) by which electric conductivity is preset became to the ultrapure water, and drying the liquid (KK).    USE - Manufacture of catalyst used for composition for gas-diffusion-electrode for membrane/electrode joined component for fuel cell stack (all claimed) of fuel cell electric vehicles and cogeneration systems.    ADVANTAGE - The method enables simple, economical and reliable manufacture of catalyst, and reduces the chlorine species content, and prevents reduction in catalyst activity.    DETAILED DESCRIPTION - Manufacture of catalyst involves forming liquid including ultrapure water, reducing agent, and an electrode catalyst precursor using chlorine-species-containing material and which has chlorine species concentration as measured by x-ray fluorescence (XRF) analysis which is equal to or more than preset chlorine species (S1) concentration which is held for preset holding time at 10-95 degrees C, forming liquid (HH) by adding ultrapure water to obtained liquid, filtrate-washing the catalyst precursor in liquid (HH) using ultrapure water, and in which the washing is repeated until below the setting value (V1) in which electric conductivity measured by the Japanese Industrial Standard testing method JIS K0552 of the filtrate obtained is preset after washing, preparing liquid (KK) in which the catalyst precursor is dispersed in the liquid as for which below the setting value (V1) by which electric conductivity is preset became to the ultrapure water, and drying the liquid (KK). The catalyst has a core-shell structure containing a support, core portion formed on the support, and shell portion formed so that one or more portion of the surface of the core portion is covered.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart explaining manufacture of catalyst. (Drawing includes non-English language text)    Catalyst precursor (BB)    Ultrapure water and reducing agent (CC)    Ultrapure water (GG)    Liquids (HH,KK)    Catalyst (LL)