A personal authentication method is provided that includes imaging, on an image sensor as a laser speckle using an optical system, light reflected from a blood vessel layer in subcutaneous and internal tissues when a laser beam is expanded and made to irradiate a finger pad, calculating a quantity that represents the rate of change with respect to time of the amount of light received for each pixel of the laser speckle, obtaining a finger pad blood flow map as a two-dimensional map of the numerical values, and comparison-checking the blood flow map against pre-registered data of individuals, wherein using a near-infrared laser beam or using this in combination with a visible laser beam, comparison-checking against pre-registered data of individuals is carried out using a pattern reflecting a fingerprint occurring within the finger pad blood flow map obtained from reflected light and, observed superimposed thereon, an internal tissue blood flow distribution pattern, and there is also provided a device used for the method.