A micro-optical grid structure is produced on a surface layer of a substrate by an embossing device and method. The embossing device includes an embossing member and a backing member, a temperature adjuster for adjusting the embossing temperature and a pressure adjuster for adjusting the pressure exerted by the embossing member and the backing member to the surface layer of the substrate. An optical measuring device is arranged to produce a diffraction signal dependent on the intensity of light diffracted from the surface of the substrate. The embossing pressure and/or temperature is/are adjusted on the basis of the diffraction signal to produce an optimal and even pattern depth of the grid structure. With the adjustment based on the diffraction signal, it is possible to avoid the sticking of the surface of the substrate to the embossing member due to too high an embossing temperature. When the pattern depth is optimal, collapse of the substrate caused by the too high embossing pressure is avoided.