Provided is a lamp assembly, including: a housing including a bottom portion and side wall portions forming a light source mount portion in a longitudinal direction, a flange portion being connected to each front end of the side wall portions and forming a first insertion portion with an inner side surface thereof being open, and a second insertion portion provided on a bottom surface of the first insertion portion; a lampshade provided therein with a light source, and coupled to the mount portion; a translucent panel slidably coupled to the first insertion portion; a packing fitted in the second insertion portion; and a press bar being inserted in the first insertion portion between an upper surface of the flange portion and the translucent panel and pressing the translucent panel and the packing, thereby fixing the translucent panel and endowing the packing with watertightness.