An illuminating lamp which can be easily assembled is provided. The illuminating lamp includes a decorative component including a mounting member mountable to an opening provided to a roof trim of a vehicle and a lens mounted on a compartment side of the mounting member, and a functional component including a light source and a holder which holds the light source and is mounted to the mounting member. The mounting member includes a flat plate to which the holder is mounted, an aperture provided at the flat plate to transmit light into the compartment, and a cover portion receiving the light source and reflecting the light of the light source into the compartment. The cover portion includes an opening portion at one end thereof along a longitudinal direction of the flat plate through which the light source is inserted along the flat plate.