A device for measuring the concentration of substance in blood that measures the concentration of substance that is included in the blood of a body, comprising:
- a laser oscillator that oscillates a first laser light having a wavelength that is within the range 2.5 μm to 12 μm, and that is absorbed by the substance;
- a light-guiding unit that guides the first laser light to the body, and guides first diffused reflected light that is generated by the first laser light from the body;
- and
- a light-detection unit that detects the light intensity of the first diffused reflected light.