In a vehicular illumination device which illuminates a lower part around an opened part of a door at a side of a vehicle, a side sill garnish is provided below the door-opened part, and a lamp and a lamp garnish which retains the lamp are arranged on a lower face of the side sill garnish. As the lamp is retained by the lamp garnish, the lamp can efficiently and appropriately illuminate an underfoot floor when a person rides on and off the vehicle. Moreover, the lamp garnish has a recess, and an edge which is provided around an opened part of the recess. As the lamp is arranged in the recess, the lamp is not visually recognized directly from the exterior of edge parts, thereby preventing a following vehicle from falsely recognizing the lamp as a backup lamp.