A method of tinning or soldering for bonding tin or solder alloy on a surface of a copper land portion or a surface of a copper and copper alloy lead portion of an electronic component, the soldering method comprising: forming a tin or solder alloy film by ejecting molten tin liquid or molten solder alloy liquid in a reservoir in a jet state onto the surface of the copper land portion or the surface of the copper and copper alloy lead portion of the electronic component to be solder-bonded by a nozzle or a slit; transporting the overflowing molten tin liquid or molten solder alloy liquid to a stirrer; characterized by: taking in copper oxide, a flux component and reaction product thereof existing on the copper land surface or the copper and copper alloy lead surface of an electronic component to be tinned or soldered that are mixed in the overflowing molten tin or molten solder alloy liquid, copper oxide, tin oxide originally existing in the molten tin or molten solder alloy liquid, or oxide of the other added metal, and a pollutant such as oxidized impurities such as iron, lead, silicon and potassium mixed in in a tiny amount into an organic fatty acid solution by stirring and mixing the molten tin or molten solder alloy liquid in contact with the organic fatty acid solution at a temperature of 180 to 350°C consisting of 1 to 80 mass% of organic fatty acid having 12 to 20 carbon number and ester synthetic oil for the rest that circulates in the stirrer to purify the molten tin liquid or molten solder alloy liquid; introducing the mixed liquid into an organic fatty acid solution reservoir; and returning a purified molten tin liquid or molten solder alloy liquid that is separated in the organic fatty acid solution reservoir according to a specific gravity difference from a bottom of the organic fatty acid solution reservoir to the reservoir of the molten tin liquid or molten solder liquid by a pump for circulation use. forming a tin or solder alloy film by ejecting molten tin liquid or molten solder alloy liquid in a reservoir in a jet state onto the surface of the copper land portion or the surface of the copper and copper alloy lead portion of the electronic component to be solder-bonded by a nozzle or a slit; transporting the overflowing molten tin liquid or molten solder alloy liquid to a stirrer; taking in copper oxide, a flux component and reaction product thereof existing on the copper land surface or the copper and copper alloy lead surface of an electronic component to be tinned or soldered that are mixed in the overflowing molten tin or molten solder alloy liquid, copper oxide, tin oxide originally existing in the molten tin or molten solder alloy liquid, or oxide of the other added metal, and a pollutant such as oxidized impurities such as iron, lead, silicon and potassium mixed in in a tiny amount into an organic fatty acid solution by stirring and mixing the molten tin or molten solder alloy liquid in contact with the organic fatty acid solution at a temperature of 180 to 350°C consisting of 1 to 80 mass% of organic fatty acid having 12 to 20 carbon number and ester synthetic oil for the rest that circulates in the stirrer to purify the molten tin liquid or molten solder alloy liquid; introducing the mixed liquid into an organic fatty acid solution reservoir; and returning a purified molten tin liquid or molten solder alloy liquid that is separated in the organic fatty acid solution reservoir according to a specific gravity difference from a bottom of the organic fatty acid solution reservoir to the reservoir of the molten tin liquid or molten solder liquid by a pump for circulation use.