Abstract: The blood flow is examined by making multifractal analysis of a blood flow velocity distribution in a vascular network and detecting a deviation of the blood flow velocity distribution from the multifractal distribution. The blood flow velocity distribution is provided as an image by irradiating laser light to the vascular network, converging, by an imaging lens, scattered laser light rays by blood cells in the blood flowing through blood vessels, detecting, by a photodetector, a speckle pattern produced owing to random interference between the scattered laser light rays and calculating the rate of change with time lapse of each speckle in the speckle pattern.