As the probe (1), the optical fiber for projection which the plane of fire which crosses the entrance place which crosses the first optical axis (11) vis-a-vis (12) the optical fiber for light absorption which it possesses in the Tip (10) with, the second optical axis (21) vis-a-vis (22) it possesses Out in the Tip (20) with, has positive refracting power, projects the light which plane of fire (22) from radiation is done Out to the measurement region of the body tissue, the light which is sent from the measurement region of the body tissue is had the entrance place (12) the glass lens which it condenses (30) with. The glass lens (30) has, the entrance place (12) and the convex surface plane of fire (22) for Out (34) with, the convex surface (34) the plane surface which was formed to opposite side (36) with, the third optical axis (31) with. The convex surface (34) the center (35) from the optical fiber for light absorption (10) the first optical axis (11) to distance (L1), that center (35) from the optical fiber for projection (20) the second optical axis (21) to distance (L2) is briefer.プローブ(1)は、第一光軸(11)に対して直交する入射面(12)を先端に有する受光用光ファイバ(10)と、第二光軸(21)に対して直交する出射面(22)を先端に有する投光用光ファイバ(20)と、正の屈折力を有し、出射面(22)から出射した光を生体組織の測定部位に投射するとともに、生体組織の測定部位から発した光を入射面(12)に集光させるレンズ(30)と、を備える。レンズ(30)が、入射面(12)及び出射面(22)に対する凸面(34)と、凸面(34)の反対側に形成された平面(36)と、第三光軸(31)と、を有する。凸面(34)の中心(35)から受光用光ファイバ(10)の第一光軸(11)までの距離(L1)が、その中心(35)から投光用光ファイバ(20)の第二光軸(21)までの距離(L2)よりも短い。
