A living body information signal processing system (100) combining organically a living body optical measurement apparatus and a brain wave measurement apparatus, the living body optical measurement apparatus (300) in which inspection light of from visible to near infrared is irradiated on a head portion of a subject (140) and the penetration light is received and which measures an optical characteristic variation induced by a brain activity inside the head portion as a living body optical signal and the brain wave measurement apparatus (400) which measures an electrical characteristic variation induced by a brain activity inside the head portion of the subject as a brain wave signal, is provided with a probe device (50) used for both apparatus; and a living body information signal processing and displaying device (200) which displays the living body optical signal corresponding to respective measurement positions from the living body optical measurement apparatus and the brain wave signal corresponding to respective measurement positions from the brain wave measurement apparatus on a common display device while correlating the respective measurement positions each other, thereby, with the system comprehensive observation of both data can be achieved.