A vehicular lighting instrument semiconductor light source light source unit, comprising: a light source portion; and a socket portion to which the light source portion is mounted, wherein the light source portion has a light emitting chip (40, 41, 42, 43, 44) of a semiconductor light source, and the socket portion is comprised of: a thermo conductive resin member to radiate to an outside a heat which is generated at the light source portion; an electric power feeding member (91, 92, 93) electrically connected to the light source portion, feeding electric power to the light source portion; and an insulation member to sheath at least a part of the electric power feeding member, and incorporate the thermo conductive resin member and the electric power feeding member (91, 92, 93) in a state in which the members are insulated from each other; characterized in that a metallic body is provided at a site corresponding to the light source portion of the thermo conductive resin member; and wherein fine irregularities are provided on a face of the metallic body, which comes into contact with at least the thermo conductive resin member, and the metallic body is insert molded in the thermo conductive resin member. a light source portion; and a socket portion to which the light source portion is mounted, wherein the light source portion has a light emitting chip (40, 41, 42, 43, 44) of a semiconductor light source, and the socket portion is comprised of: a thermo conductive resin member to radiate to an outside a heat which is generated at the light source portion; an electric power feeding member (91, 92, 93) electrically connected to the light source portion, feeding electric power to the light source portion; and an insulation member to sheath at least a part of the electric power feeding member, and incorporate the thermo conductive resin member and the electric power feeding member (91, 92, 93) in a state in which the members are insulated from each other; characterized in that a metallic body is provided at a site corresponding to the light source portion of the thermo conductive resin member; and wherein fine irregularities are provided on a face of the metallic body, which comes into contact with at least the thermo conductive resin member, and the metallic body is insert molded in the thermo conductive resin member. a thermo conductive resin member to radiate to an outside a heat which is generated at the light source portion; an electric power feeding member (91, 92, 93) electrically connected to the light source portion, feeding electric power to the light source portion; and an insulation member to sheath at least a part of the electric power feeding member, and incorporate the thermo conductive resin member and the electric power feeding member (91, 92, 93) in a state in which the members are insulated from each other; characterized in that a metallic body is provided at a site corresponding to the light source portion of the thermo conductive resin member; and wherein fine irregularities are provided on a face of the metallic body, which comes into contact with at least the thermo conductive resin member, and the metallic body is insert molded in the thermo conductive resin member.