To provide a structure of an electrode catalyst, which is adopted in an electrochemical device using an ionic liquid as an electrolyte and is used for advancing an electrode reaction smoothly.

The structure of the electrode catalyst is adopted in the electrochemical device using the ionic liquid as the electrolyte and has an electrode catalyst layer which is formed on an electrode base material and in which a material for mitigating the poisoning of the electrode catalyst is mixed. The material for mitigating the poisoning of the electrode catalyst is an alkali metal or an alkaline-earth metal. The alkali metal to be used is lithium, sodium, potassium, rubidium, cesium, francium, etc. The alkaline-earth metal to be used is beryllium, magnesium, calcium, strontium, barium, radium, etc.