The light irradiation unit that irradiates near infrared light (660 ± 60nm) wavelength λ2 and a second (805 ± 30nm) wavelength λ1 of the first blood and (3), near infrared light irradiated on the blood a light receiving portion of the reflected light (4), the light irradiation section (3) light receiving part (4) are arranged substantially in parallel, the center (7) tip of the light irradiating section (3) (7C) The optical transceiver (2), what was the 0.9~3.0mm interval (8C) center (8) tip (4) receiving part (SD), and the light emitting element and receiving (13) The provided separately electronic circuitry including (14) from (30) elements, each illumination optical fiber (5) receiving optical fiber the light irradiation section (3) of the light receiving part (4) (6) blood characteristic measuring probe is configured and coated with liquid-tight sheath (21) (1).血液中に第1の波長λ1(805±30nm)及び第2の波長λ2(660±60nm)の近赤外光を照射する光照射部(3)と、前記血液に照射された近赤外光の反射光の受光部(4)を有し、この光照射部(3)と受光部(4)はほぼ並列に配置され、光照射部(3)の先端部(7)の中心(7C)と受光部(4)の先端部(8)の中心(8C)の間隔(SD)を0.9~3.0mmにしたものを、光送受信部(2)とし、発光素子(13)及び受光素子(14)を含む電子回路部(30)から分離して設け、前記光照射部(3)および前記受光部(4)がそれぞれ照射用光ファイバ(5)および受光用光ファイバ(6)により構成され、シース(21)で液密的に被覆された血液特性測定プローブ(1)。
