An electroless plating solution is accommodated in a plating tank of an electroless plating apparatus. A reference electrode and a counter electrode are immersed in the electroless plating solution. A conductive member is provided to be electrically in contact with a conductive portion of a long-sized substrate. The conductive member, the reference electrode, and the counter electrode are connected to a potentiostat. A main control device controls the potential of the conductive portion of the long-sized substrate by a potentiostat such that the potential of the conductive portion of the long-sized substrate with respect to a potential of the reference electrode is equal to a potential of the independent portion of the long-sized substrate with respect to the potential of the reference electrode.

Claims data not available