Optical information recording medium, its information recording/reproducing method, and information recording/reproducing device

An optical information recording medium includes a substrate, n information recording layers provided on the substrate, and spacer layers, each of which is provided so as to be interposed between the information recording layers, wherein each of (n−1) or more of the information recording layers has a layer number information part that is formed in correspondence with one or more recording marks X and contains layer number information, where n represents an integer of not less than 2, and the layer number information is information used for determining which a given information recording layer is among the n information recording layers. Each recording mark X has a length in a circumferential direction longer than a length of a recording mark Y used for recording another information in the information recording layers.