In a personal authentication method using the subcutaneous bloodstream measurement where an expanded laser beam is irradiated onto a finger pad, light reflected from a subcutaneous blood vessel layer is imaged on an image sensor as a laser speckle using an optical system, 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 is calculated, the values are used as a two-dimensional map to obtain a map showing the bloodstream of the finger pad, and the bloodstream map is comparison-checked against pre-registered data of individuals, the laser speckle is imaged on the image sensor using a region separate from a region irradiated by the laser beam as an observation region of the image sensor. A device for use in the method is also provided. Relating to a method and device for authentication using, e.g., a finger print pattern on the basis of the laser speckle, an improved technique capable of extracting, e.g., the finger print pattern accurately is provided.