Disclosed is a method for apprehending the mental state such as feelings or emotions of an individual using non-invasive biological light measurement technology. The disclosed biological light measurement device, which has a light-irradiation means and a light-detection means, presents a plurality of differing tasks (at least a first task and a second task) to a test subject, a hemoglobin signal based on changes in the concentration of oxygenated hemoglobin and deoxygenated hemoglobin inside the aforementioned test subject is calculated from the strength of the light detected by the aforementioned light-detection means, and a relative value using the hemoglobin signal at a predetermined measurement point with respect to the first task, and the hemoglobin signal at a different predetermined measurement point with respect to the second task is calculated.
BIOLOGICAL LIGHT MEASUREMENT DEVICE