A lamp assembly to be attached with a reinforcement through an opening formed in a roof panel is provided. A clip to be locked with the reinforcement is provided in the lamp assembly. The clip includes a base portion connected to the housing, an inverted U-shape portion connected to the base portion, a lock connected to the inverted U-shape portion, a projecting piece projected from a lower end of the lock, an extension portion extended further downwards from the projecting piece, and a side projecting piece formed on a side surface of the extension portion at a lower portion. A front projecting piece which faces the side projecting piece with a space provided therebetween is formed on the housing. The side projecting piece comes in contact with the front projecting piece in a state where the clip is locked on a circumferential edge of an opening of the reinforcement.