There is provided a forming mold 40 made on the basis of a standard more reliable than an average roughness of a surface of a metal film that generates surface plasmon resonance, the forming mold being capable of improving an S/N ratio of an optical element 20. A forming mold 40 for a substrate 21 of an optical element 20 used for measurements utilizing surface plasmon, wherein an Spc value of a molding surface 51t for transferring a shape onto a surface 21a of the substrate 21 on a side facing an object to be measured is equal to or less than 100 [1/mm].