Method of producing copper powder and copper powder

A method of producing copper powder is provided that uses electrolytic cuprous oxide as the starting material for the production of copper powder suitable for a conductive filler whose particles have an average particle diameter of not greater than 1 μm or even not greater than 0.5 μm and are of uniform size. In one aspect, the method comprises a step of mixing cuprous oxide with a reducing agent in a liquor in which a protective colloid is present and to which a water-soluble copper salt has been added and in another aspect comprises a step of reducing a water-soluble copper salt in a liquor in which a protective colloid is present, thereby forming a slurry, and a step of reducing cuprous oxide in the presence of the slurry. As the water-soluble copper salt can be used, for example, 0.1-20 moles of a monovalent copper salt such as cuprous chloride per 100 moles of the cuprous oxide. As the protective colloid can be used 1-40 parts by mass of a water-soluble polymer per 100 parts by mass of the cuprous oxide.