Disclosed is an optical measurement system (1) provided with a main optical measurement device (10) and a portable optical measurement device (40). The optical measurement system (1) is characterized in that the portable optical measurement device (40) is provided with a second case (41) portable by the subject, C second light sending means (12) for illuminating the subject, D second light receiving means (13) for receiving light emitted from the subject, a second holder (60) worn on the head of the subject and having at least (C+D) through holes therein, a control unit (51) for acquiring measurement data relating to a brain activity while controlling the second light sending means (12) and the second light receiving means (13), and a communication unit (46) capable of communicating with the main optical measurement device (10), that (C+D) > (A+B) is satisfied, and that the communication unit (46) of the portable optical measurement device (40) transmits the measurement data acquired by the control unit (51) of the portable optical measurement device (40) to the main optical measurement device (10).
