PURPOSE: To facilitate mass productivity and production and to increase strength by using a protective plate having a microwave adsorptive layer, joining the protective plate and recording part and irradiating microwaves thereto to weld both.

CONSTITUTION: Pregrooves 31 having a recessed shape are provided on the surface of a substrate 3 and as a result the substrate 3 is welded and united to the protective plate 100 installed with the microwave absorptive layer 4 at the points of the projections formed on the surface of the substrate. The recording part of the recording layer 5 positioned in the recesses of the substrate 3 can be sealed by having a gap from the protective plate 100 without tightly contacting therewith. Such recording part is used as a recording rack part. Writing and reading light are usually irradiated thereto from the smooth rear surface side of the substrate 3. The writing sensitivity and read-out S/N ratio are thereby improved and the control signal for tracking is increased; further the production is easy and the mass productivity is high. The resulted medium is substantially strong.