An electrode device is provided with a closed part facing a bottom part of a bottomed hole when inserted inside the bottomed hole, and a flow through hole linking the inside and outside of the electrode device is formed in the electrode device. When surface treatment is implemented on the inner wall surface of the bottomed hole, the hollow electrode device is inserted into the inside of the bottomed hole, the electrolytic treatment solution is made to flow through the space inside the bottomed hole, and power is applied across the electrode device and the inner wall surface of the bottomed hole. The closed part faces the bottom part of the bottomed hole as an electrode across a prescribed surface area; therefore, electroplating at the bottom part of the bottomed hole proceeds to the same extent as other sites.