To provide an image display in which an image having high contrast and reduced illumination unevenness is displayed.

An illumination optical system that illuminates a reflection type light modulation element via a polarization separation plane by using a light flux from a light source, comprises compression means in which when a cross-section plane in parallel with a normal line of the polarization separation plane and a normal line of the light modulation element is taken as a second cross-section plane, and a cross-section plane perpendicular to the second cross-section plane, including an optical axis of the illumination optical system is taken as a first cross-section plane, a refracting power arrangement in the first cross-section plane and a refracting power arrangement in the second cross-section plane are different from each other, and a width in the second cross-section plane of the light flux from the light source is thereby compressed.