To provide an illuminator and an illuminating method by which the uniformity of light intensity is enhanced by stably and efficiently suppressing occurrence of an interference fringe with a simple and compact configuration, and also to provide a display device high in uniformity, and a processing device.

The illuminator is provided with: a light source to emit coherent light; a lens array having a plurality of microlenses arranged at pitch p; and a polarized light conversion element which is provided between the light source and the lens array, on which light emitted from the light source is made incident, which converts the incident light so that polarizing patterns of the light to be made incident on the microlenses adjacent to each other differ from each other, and makes the converted light incident on the microlenses.