The present technology relates to an electromagnetic wave processing device that enables suppression of a ripple. Provided are a photoelectric conversion element, a narrow band filter stacked on a light incident surface side of the photoelectric conversion element and configured to transmit an electromagnetic wave having a desired wavelength, and interlayer films respectively formed above and below the narrow band filter, and the narrow band filter is formed in a shape with a level difference. The level difference is formed for each photoelectric conversion element. Alternatively, the level difference is formed between the photoelectric conversion elements and in the interlayer film. The present technology can be applied to an imaging element or a sensor using a plasmon filter or a Fabry-Perot interferometer.