A recording medium in a card form, the recording medium having a front face, a back face and end faces and comprising: a substrate; and a color development layer including a plurality of color development layers (10BL, 10BM, 10BH) laminated on the substrate and being provided with a plurality of lines for security (13A2 - 13E2) characterized in that each of the plurality of lines extends in a first direction from at least one of the end faces of the recording medium along a lamination surface of the color development layer that is laminated on the substrate, the lamination surface being parallel to the front face of the recording medium, such that each of the lines for security (13A2 - 13E2) is optically identifiable from the front face of the recording medium, each of the plurality of lines for security (13E2 - 13E2) extends in a second direction along at least one of the end faces of the recording medium, from which the plurality of lines for security (13A2 - 13 E2) extend in the first direction, across an entire thickness of one of the color development layers (10BL, 10BM, 10BH) such that presence of the lines for security is optically identifiable at the end face, wherein the plurality of lines for security (13A2 - 13E2) are arranged at positions based on a predetermined information code on the end face, the plurality of lines for security (13A2 - 13E2) correspond to a single information code and are arranged at positions based on this information code in a thickness direction of the end face, and the plurality of color development layers (10BL, 10BM, 10BH) are configured to differ from each other in energy threshold necessary for color development and in color given by color development. a substrate; and a color development layer including a plurality of color development layers (10BL, 10BM, 10BH) laminated on the substrate and being provided with a plurality of lines for security (13A2 - 13E2) characterized in that each of the plurality of lines extends in a first direction from at least one of the end faces of the recording medium along a lamination surface of the color development layer that is laminated on the substrate, the lamination surface being parallel to the front face of the recording medium, such that each of the lines for security (13A2 - 13E2) is optically identifiable from the front face of the recording medium, each of the plurality of lines for security (13E2 - 13E2) extends in a second direction along at least one of the end faces of the recording medium, from which the plurality of lines for security (13A2 - 13 E2) extend in the first direction, across an entire thickness of one of the color development layers (10BL, 10BM, 10BH) such that presence of the lines for security is optically identifiable at the end face, wherein the plurality of lines for security (13A2 - 13E2) are arranged at positions based on a predetermined information code on the end face, the plurality of lines for security (13A2 - 13E2) correspond to a single information code and are arranged at positions based on this information code in a thickness direction of the end face, and the plurality of color development layers (10BL, 10BM, 10BH) are configured to differ from each other in energy threshold necessary for color development and in color given by color development.