A dynamic light scattering measurement apparatus using a phase modulation type interference method comprises an optical coupler 5 for dividing light from a low coherent light source 2, a converging lens 10 for irradiating one of the lights divided by the optical coupler 5 to a sample medium 9, phase modulators 7, 8 for modulating the phase of the other of the lights divided by the optical coupler 5, a spectrum measurement means 12 for measuring the spectrum of the interference light of the phase-modulated reference light and the scattered light outgoing from the sample medium 9, and an analyzing means for measuring the dynamic light scattering of particles of the sample medium based on at least any one of the first order spectrum corresponding to the basic frequency of the phase-modulating signal or a higher order spectrum corresponding to a frequency equal to two, three or the like times the basic frequency appearing in the interference light spectrum measured by the spectrum measurement means 12. The amount s/L obtained by normalizing the light path length s within the sample medium by the mean free path L of the particles is set to be not more than 3. Dynamic properties of a high concentration medium can be measured with high precision based on the scattered light from the high concentration medium.