A chemiluminescence measurement apparatus comprising: a support member suitable for supporting a cartridge for measuring a test substance contained in a specimen by chemiluminescence measurement; a motor (40, 171) configured to rotate the support member so as to rotate the cartridge such that a process required for the chemiluminescence measurement proceeds in the cartridge; a light receiver (70a, 144a) configured to receive light generated by chemiluminescence in the cartridge that is supported by the support member rotated by the motor (40, 171); a light-shielding portion; wherein the support member, the cartridge, when mounted to the support member, and a light receiving surface of the light receiver (70a, 144a) are disposed inside a dark space surrounded by the light-shielding portion; wherein the motor (40, 171) is disposed outside the dark space; characterized in that: the chemiluminescence measurement apparatus comprises a ventilator for dissipating heat generated from the motor (40, 171) to outside of the apparatus and a reflector configured to guide light toward the light receiver, wherein the reflector has a hole that penetrates therethrough in a vertical direction, the reflector being positioned such that the cartridge, when mounted to the support member, is on one side of the reflector and the light receiving surface is on another side of the reflector such that light emitted in the cartridge passes through the hole to the light receiving surface, wherein the light-shielding portion is configured to surround the cartridge, when supported by the support member, the light receiving surface of the light receiver, and the reflector, wherein the light receiver is capable of performing photon counting and the ventilator is disposed outside of the dark space (81, 340). a support member suitable for supporting a cartridge for measuring a test substance contained in a specimen by chemiluminescence measurement; a motor (40, 171) configured to rotate the support member so as to rotate the cartridge such that a process required for the chemiluminescence measurement proceeds in the cartridge; a light receiver (70a, 144a) configured to receive light generated by chemiluminescence in the cartridge that is supported by the support member rotated by the motor (40, 171); a light-shielding portion; wherein the support member, the cartridge, when mounted to the support member, and a light receiving surface of the light receiver (70a, 144a) are disposed inside a dark space surrounded by the light-shielding portion; wherein the motor (40, 171) is disposed outside the dark space; characterized in that: the chemiluminescence measurement apparatus comprises a ventilator for dissipating heat generated from the motor (40, 171) to outside of the apparatus and a reflector configured to guide light toward the light receiver, wherein the reflector has a hole that penetrates therethrough in a vertical direction, the reflector being positioned such that the cartridge, when mounted to the support member, is on one side of the reflector and the light receiving surface is on another side of the reflector such that light emitted in the cartridge passes through the hole to the light receiving surface, wherein the light-shielding portion is configured to surround the cartridge, when supported by the support member, the light receiving surface of the light receiver, and the reflector, wherein the light receiver is capable of performing photon counting and the ventilator is disposed outside of the dark space (81, 340). the chemiluminescence measurement apparatus comprises a ventilator for dissipating heat generated from the motor (40, 171) to outside of the apparatus and a reflector configured to guide light toward the light receiver, wherein the reflector has a hole that penetrates therethrough in a vertical direction, the reflector being positioned such that the cartridge, when mounted to the support member, is on one side of the reflector and the light receiving surface is on another side of the reflector such that light emitted in the cartridge passes through the hole to the light receiving surface, wherein the light-shielding portion is configured to surround the cartridge, when supported by the support member, the light receiving surface of the light receiver, and the reflector, wherein the light receiver is capable of performing photon counting and the ventilator is disposed outside of the dark space (81, 340).