1. A method for acquiring personal identification data to identify a specified person by measuring subcutaneous bloodstream, comprising the steps of: irradiating a laser beam onto at least a part of a fingertip surface or a palm; imaging light reflected from subcutaneous blood vessels at an irradiation spot to which a laser beam is irradiated in the laser beam-irradiating step by receiving the same on an image sensor as laser speckles; calculating a change ratio of a light-receiving amount at respective pixels of the laser speckles; preparing a two-dimensional bloodstream map of the irradiation spot based on numerical values obtained in the step of calculating a change ratio of a light-receiving amount; and storing a ridge-and-recess pattern of the irradiation spot appearing in the two-dimensional bloodstream map as personal identification data.