PURPOSE: To accurately perform a beam lithography by bringing a positioning member securing a central opening by using a rodlike or platelike bridge for specifying flatness into contact with a lithography face in a substrate holding cassette device used for an electron beam or ion beam lithography apparatus.

CONSTITUTION: A substrate 3 to be subjected to a lithography is engaged within the opening of a substrate holding cassette device 10, and its rear face is retained through a central retainer 4 by a leaf spring 6. In this case, the spring 6 is formed in a curved face curved upward, and its outer edge is secured by a securing groove 7 formed on the inner periphery of the cassette device 10. Thereafter, the surface of the substrate 3 exposed on the surface and the end surface of the device 10 are retained by a positioning member 8, and a distortion generated on the lithography face of the substrate 3 is eliminated. Here, a photodetecting opening 5 is provided on the member 8, and supported in a cross state by a rodlike or platelike material made of Al, Ti, Mo, etc., having approx. 50μm of thickness and approx. 1000μm of height, not to disturb the lithography. Thus, its flatness can be accurately specified without reducing the lithography area.