The present technique relates to a demodulation device, a demodulation method and a program capable of realizing a demodulation process at a rate equivalent to a case where I and Q channel signals are not inverted, even when the I and Q channel signals are inverted. An optical near-field is generated by using the conductive scatterer having a width that gradually becomes smaller toward a vertex at which the optical near-field is generated. The multi-layer mirrors consist of N and M period of quarter wavelength layers where N and M are integers, or integers plus.