Disclosed is an instrument illumination device enabling homogeneous illumination light in a broad area, without increasing the number of light sources, and thereby enhancing the freedom degree of the ornamental designing process. An instrument housing includes a bottom face having LEDs disposed thereon and an illumination area including a main illumination area having a main dial for displaying a revolution on the dial plate covering a front opening and an auxiliary illumination area having an auxiliary dial for displaying water temperature. The main illumination area is in the shape of a ring having a cut-out at a lower part thereof, and the auxiliary illumination area fills the cut-out connecting the main illumination area. Illumination light from the LEDs illuminates an entire face of the illumination area in the ring shape from a rear side thereof as backlight.