An illumination device includes an illumination lamp installed to a device housing, a sensor for use in controlling the lighting operation of the illumination lamp, and a sensor attachment unit through which the sensor is detachably attached to the device housing such that a sensing unit of the sensor is exposed to the outside. The illumination device further includes a decoration member for attachment to the sensor attachment unit when the sensor is not attached to the sensor attachment unit, the decoration member having substantially the same outward appearance as that of the sensor. The sensor and the decoration member are interchangeably attached to the sensor attachment unit.