A quantum efficiency measurement method includes the steps of: disposing a sample at a predetermined position in an integrator having an integrating space; applying excitation light to the sample and measuring a spectrum in the integrating space as a first spectrum through a second window; configuring an excitation light incident portion so that excitation light after having passed through the sample is not reflected in the integrating space; applying the excitation light to the sample and measuring a spectrum in the integrating space as a second spectrum through the second window; and calculating a quantum efficiency of the sample based on a component constituting a part of the first spectrum and corresponding to a wavelength range of the excitation light, and a component constituting a part of the second spectrum and corresponding to a wavelength range of light generated by the sample from the received excitation light.