To perform plating treatment while stably applying tenson to a thin sheet having flexibility.

The substrate outer edge part of a thin sheet having flexibility is sandwiched with a grasping unit installed in the supporting frame of a thin sheet tension application fixture, and is applied with tension while being held. The thin sheet having flexibility is adsorbed on the adsorption table of a fixture detachable device for thin sheet plating, and while holding the same, the substrate edge of the thin sheet having flexibility is sandwiched with the upper frame and the lower frame of a fixture for thin sheet plating to close up the upper frame and the lower frame. The four corners of the closed upper frame and lower frame are pressed from the upper and lower parts with a clasp and are fixed, then the grasping unit is removed from the thin sheet having flexibility, and the thin sheet tension application fixture is separated to obtain a structure in which the thin sheet having flexibility is fixed while holding the tension with the fixture for thin sheet plating. The structure is installed in the fixture for plating, and the fixture for thin sheet plating is dipped into the plating tank together with the thin sheet having flexibility.