An illumination device emits illumination light and has a light source arranged inside a housing generating illumination light; a diffusing panel attached to the housing; and a projector inside a space formed by the housing and a part of the diffusing panel and projecting an image onto a projection surface. An optical unit is arranged so that an incident direction of a light flux incident from a display element provided in the projector onto a projection optical system of the projector is substantially parallel to a horizontal plane or in a direction closer to a direction parallel to the horizontal plane than a vertical direction, or in so that an optical axis of the projection optical system on which the light flux from the display element is substantially parallel to the horizontal plane or in a direction closer to a direction parallel to the horizontal plane than the vertical direction.