To provide a shape inspecting method, capable of simply and highly accurately inspecting the surface shape of a plastic body, even it is a plastic body with a fine surface shape such as a reflecting plate to be used for a reflecting-type liquid crystal display device, and to provide its substrate material.

A resin material is applied to a plastic body (substrate material 1) formed into a prescribed shape, hardened and is integrated under conditions which does not change the shape of the plastic body. Then the plastic body and hardened resin material 2 are cut to prepare a sample piece, and the cross- sectional shape of the plastic body is observed through the use of the sample piece.