a lamp module for receiving therein a lamp as a light source; and

an enclosure for allowing an optical axis of the light source from said lamp module to be fixedly aligned to a predetermined direction by covering, with a lid, an opening of a lamp module receiving portion for receiving therein said lamp module;

said lamp module having two positioning pins embedded therein in a substantially vertical direction to said optical axis for controlling movement of said optical axis in a horizontal plane, and a boss allowing a screw to pass through the boss in parallel with an embedded position of said pins;

said enclosure having a first rib extended inward from a back side of a ceiling face that is a bottom face of said lamp module receiving portion and three second ribs, each of the three second ribs having a substantially U-shaped cross-section, embedded upright from said lid in a triangularly arrangement such that when said lamp module is received in said lamp module receiving portion, a small gap is formed between said enclosure and said lamp module; and

said lamp module receiving portion having a positioning portion including positioning holes allowing the two positioning pins to be inserted therein and a socket portion provided with a female screw engaging the female screw passed through said boss,

while being properly positioned by said positioning pins inserted into the positioning holes of said positioning portion, said lamp module is received into said lamp module receiving portion with a movement of said lamp module in a horizontal plane controlled by the screw passed through said boss and engaged with the female screw in the socket portion, and said opening in said lamp module receiving portion is covered with the lid fastened with screws such that movement of said lamp module in a vertical direction is controlled by said first rib and said second ribs in order for the optical axis to be fixed.