To solve a problem that light from a light source forms a point shape, or that visibility is reduced according to angles since diffusion characteristics (expansion) is low in a conventional illumination device.

In the illumination device, a translucent plate is arranged on a front face of the light source, and the translucent plate includes: two or more strips of slender protruding strips on either one face of the inner face on the light source side or the outer face on a side opposite to the light source; and two or more slender protruding strips in a direction crossing a slender direction of the convex strip on the other face. The translucent plate can be a one-sheet plate or a two-sheet plate of the inner plate and the outer plate. The light source can be arranged in one row or two or more rows with a spacing. In this case, two or more strips of slender convex strips are installed in the arrangement direction of the light source on either one face of the inner face on the light source side of the translucent plate and the outer side opposite to the light source; and two or more strips of slender convex strips in a direction crossing the arrangement direction of the light source on the other face. The light source can be an LED, an incandescent bulb, and a beam lamp or the like.