Multi-layer information recording medium

A multi-layer information recording medium comprising:

• a plurality of recording layers, each recording layer being made from a material of which reflectance changes upon radiation of a light beam, information being writable in each recording layer as a result of reflectance change made in each recording layer, each recording layer having at least one of at least one groove and at least one pit;
• at least one spacer layer, each of the at least one spacer layer being interposed between two adjacent recording layers of the plurality of recording layers;
• an information rewritable region defined in a first recording layer of the plurality of recording layers, the first recording layer being a layer in which the information is to be written, the information rewritable region being used as a trial recording region when determining a recording condition of the first recording layer;
• and
• a window region defined in a second recording layer of the plurality of recording layers adjacent to the first recording layer for passing the light beam to the information rewritable region and imparting first diffraction to the passing light beam when determining the recording condition of the first recording layer, the second recording layer having the window region and a remaining portion, the first diffraction effect being different from a second diffraction imparted from the remaining portion of the second recording layer.