Substance-in-blood concentration measurement method

A substance-in-blood concentration measurement method for measuring concentration of a substance in blood of a living body, comprising:

• placing the living body that includes a measurement target portion;
• irradiating the measurement target portion with a laser beam from a laser;
• wherein the measurement target portion is a portion of the living body inwards of an epidermis;
• optically forming an image of light reflected from the measurement target portion onto a photodetector using a first lens disposed between the measurement target portion and the photodetector;
• and
• receiving the reflected light with the photodetector and detecting intensity of the reflected light, and
• further comprising, prior to optically forming the image, adjusting an optical path length from the measurement target portion to the photodetector so that the light reflected from the measurement target portion forms a focused image on the photodetector, wherein
• the photodetector is a two-dimensional infrared sensor array in which a plurality of light receiving elements capable of detecting mid-infrared light are arranged in a matrix on a light receiving surface.