Provided is an electrode catalyst that can exhibit sufficient performance, is suitable for mass production, and is suitable for reducing production costs, even when containing a relatively high concentration of chlorine. The electrode catalyst has a core-shell structure including a support; a core part that is formed on the support; and a shell part that is formed so as to cover at least one portion of the surface of the core part. A concentration of bromine (Br) species of the electrode catalyst as measured by X-ray fluorescence (XRF) spectroscopy is 500 ppm or less, and a concentration of chlorine (Cl) species of the electrode catalyst as measured by X-ray fluorescence (XRF) spectroscopy is 8,500 ppm or less.