An illumination device includes a light source for emitting a light flux having a solid angle; an optical element for converging the light from the light source in at least one direction to convert the light into parallel light; and a fly-eye lens for allowing incidence of the parallel light from the optical element to guide uniform light to an area for illumination. Assuming that a certain number of lens cells in the fly-eye lens in a column direction or a row direction are defined as a lens cell unit, one of the lens cell units is relatively displaced with respect to the other one of the lens cell units in the column direction or the row direction, and the number of steps for displacement among the lens cell units in the fly-eye lens is set to 2 or more.