A light source unit for a vehicle lamp which is detachably attachable to an attachment hole formed in a lighting body for a vehicle, the light source unit comprising: a circuit board which is disposed on a forward-side of the light source unit and on a front surface of which four light emitting devices (5a, 5b, 5c, 5d) are disposed at each of four directions with respect to a center thereof; and a case that is located rearward of the circuit board and that includes a radiating section, constituted by a heat sink, wherein the case has a structure in which the heat sink formed of a metal material and a socket formed of an insulating resin material are provided, and the heat sink is integrally attached to an inner side of the socket, wherein the socket has a front wall section located rearward of the circuit board, a circumferential wall section having a substantially cylindrical shape and surrounding a periphery of the front wall section on a back surface side, a front cylindrical section having a substantially cylindrical shape and protruding forward from a front surface side of the front wall section, and a through-hole passing through the front wall section inside the front cylindrical section, wherein the heat sink has a protrusion that is located rearward of the front wall section of the socket and that protrudes forward from a front surface side of a front wall section of the heat sink, wherein the protrusion of the heat sink is integrally attached to an inner side of the socket in a state in which the protrusion passes through the through-hole, wherein the circuit board is attached to a front surface of the protrusion in a state in which the circuit board is electrically insulated, wherein a reflector installed on the circuit board so as to surround the four light emitting devices (5a, 5b, 5c, 5d) is provided on a forward-side surface of the circuit board, wherein regions where the four light emitting devices (5a, 5b, 5c, 5d) are mounted on the front surface of the circuit board include (i) four side areas (B1, B2, B3, B4) in which the four light emitting devices (5a, 5b, 5c, 5d) are disposed, (ii) one center area disposed at a center of the four side areas (B1, B2, B3, B4), and (iii) four corner areas (C1, C2, C3, C4) disposed at corner sections next to the four side areas (B1, B2, B3, B4), the four side areas (B1, B2, B3, B4) being leftward and rightward side areas and upward and downward areas with regard to the center area, and wherein the reflector includes eight first reflective surfaces provided to divide spaces between each of the side areas (B1, B2, B3, B4) and the corner areas (C1, C2, C3, C4), and four second reflective surfaces that extend along sides of each of the side area (B1, B2, B3, B4) opposite to the center area. a circuit board which is disposed on a forward-side of the light source unit and on a front surface of which four light emitting devices (5a, 5b, 5c, 5d) are disposed at each of four directions with respect to a center thereof; and a case that is located rearward of the circuit board and that includes a radiating section, constituted by a heat sink, wherein the case has a structure in which the heat sink formed of a metal material and a socket formed of an insulating resin material are provided, and the heat sink is integrally attached to an inner side of the socket, wherein the socket has a front wall section located rearward of the circuit board, a circumferential wall section having a substantially cylindrical shape and surrounding a periphery of the front wall section on a back surface side, a front cylindrical section having a substantially cylindrical shape and protruding forward from a front surface side of the front wall section, and a through-hole passing through the front wall section inside the front cylindrical section, wherein the heat sink has a protrusion that is located rearward of the front wall section of the socket and that protrudes forward from a front surface side of a front wall section of the heat sink, wherein the protrusion of the heat sink is integrally attached to an inner side of the socket in a state in which the protrusion passes through the through-hole, wherein the circuit board is attached to a front surface of the protrusion in a state in which the circuit board is electrically insulated, wherein a reflector installed on the circuit board so as to surround the four light emitting devices (5a, 5b, 5c, 5d) is provided on a forward-side surface of the circuit board, wherein regions where the four light emitting devices (5a, 5b, 5c, 5d) are mounted on the front surface of the circuit board include (i) four side areas (B1, B2, B3, B4) in which the four light emitting devices (5a, 5b, 5c, 5d) are disposed, (ii) one center area disposed at a center of the four side areas (B1, B2, B3, B4), and (iii) four corner areas (C1, C2, C3, C4) disposed at corner sections next to the four side areas (B1, B2, B3, B4), the four side areas (B1, B2, B3, B4) being leftward and rightward side areas and upward and downward areas with regard to the center area, and wherein the reflector includes eight first reflective surfaces provided to divide spaces between each of the side areas (B1, B2, B3, B4) and the corner areas (C1, C2, C3, C4), and four second reflective surfaces that extend along sides of each of the side area (B1, B2, B3, B4) opposite to the center area.