The position of blood vessels can be more appropriately specified by means of appropriately selecting, on the basis of the conditions and components utilized, an angle ± between a light emitting unit optical axis J121 of a near-infrared light emitting unit 121 and a normal line N1 of an irradiated surface P1, an angle ² between an optical axis J123 of a light receiving side lens 123c and the normal line N1 of the irradiated surface P1, and an angle ³ between a light receiving surface P3 of a photodiode array 123 and the light receiving unit optical axis J123. Thus, the subcutaneous blood vessel depth in the direction of the normal line N1 from the irradiated surface P1 can be specified based on changes in illumination intensity in a photodiode array 123f. Consequently, the position of subcutaneous blood vessels can be easily specified.
