To provide the using method of a metal system catalyst when a reaction temperature exceeds the melting point of the metal system catalyst to be applied in a chemical reaction.

The using method of the catalyst, wherein when the metallic catalyst (containing a mixture of a single metal, an alloy and a plurality of metals and metal salts) in solid state at a normal temperature is applied, the metallic catalyst is used in liquid while the catalyst is kept at the melting point or at the melting point or higher is provided.