Illumination device, illumination method, and image projection device using same

The objective of the invention is to provide an illumination device and an illumination method that are highly efficient, and an image projection device using the same. In order to achieve the above objective, an illumination device comprises a light source and a light collection body whereby light from the light source is collected and sent out. The light collection body has an entrance surface on the light source side, an exit surface wherefrom the light is sent out, and a side surface between the entrance surface and the exit surface. The side surface is constituted in such a manner as to have a plurality of curved surface shapes wherein the shapes of the curved surfaces are different, and each curved surface is distanced from an optical axis directed orthogonally to the light-emitting surface of the light source, increasingly from the center of the light source, in the direction oriented from the entrance surface to the exit surface. Another illumination device comprises: a light source; a light integrator for homogenizing via internal surface reflection the light from the light source; a lens whereby the light exiting from the light integrator is converted into approximately parallel light; and a reflective parabolic surface disposed outside of the lens and converting the light from the light integrator into an approximately parallel light. The configuration of this illumination device is such that, in the lens optical axis direction, the surface of the lens on the light integrator side is disposed more to the light integrator side than the edge of the reflective parabolic surface on the side facing away from the light integrator.