Provided is a light measurement device capable of obtaining reproducible measurement data without the necessity for bringing a subject into the state of performance of a task such as finger movement many times, the measurement data having no variation and less affected by Mayer Wave and the like caused by respiration, blood pressure, and the like other than the performance of the task. Specifically provided is a light measurement device (1) which is provided with a light transmission/reception unit controller (4) for acquiring received light amount information relating to a measurement site of the brain of a subject and a calculation unit (31) for calculating the amount of change in hemoglobin concentration, and obtains measurement data indicating the change with lapse of time in the variation amount of hemoglobin concentration during the execution of a task period in which the subject is being continuously loaded, the light measurement device being characterized by being provided with a biomonitor (60) which is disposed on the surface of the skin of the subject and detects biological information relating to the heartbeat, blood pressure, or respiration of the subject, a biomonitor control unit (32) for obtaining the biological information from the biomonitor (60), and a task period start time determination unit (35) for determining the start time of the task period on the basis of the biological information.
