In-plane uniformity of a membrane electroplated on a polygon substrate is improved. An electroplating device includes an anode holder configured to hold an anode, a substrate holder configured to hold a polygon substrate, and a regulation plate provided between the anode holder and the substrate holder. The regulation plate has a body portion having a first polygon opening following an outer shape of the polygon substrate, and wall portions protruding on a substrate holder side from edges of the first polygon opening. The wall portions protrude over a first distance on the substrate holder side in first regions which contain middle portions of sides of the first polygon opening, and are notched in second regions which contain corner portions of the first polygon opening, or protrude over a second distance smaller than the first distance on the substrate holder side.