A quantum-yield measurement device 1A comprises a dark box 5; a light generation unit 6, having a light exit part 7, for generating the pumping light L1; a light detection unit 9, having a light entrance part 11, for detecting the light to be measured L2; an integrating sphere 14, having a light entrance opening 15 for the light L1 to enter and a light exit opening 16 for the light L2 to exit; and a movement mechanism 30 for moving a sample container 3, the part 7, and the part 11 such that the container 3 attains each of a first state of being located inside of the sphere 14 and a second state of being located outside of the sphere 14 and causing the part 7 and part 11 to oppose the opening 15 and opening 16, respectively, in the first state.