Or light transmitting probe 12, and a probe mounting part 161a of the two, is irradiated with light from the tip to the probe mounting section 161a, a light receiving probe 13 for receiving the light from the tip is inserted from above, of the subject at least A holder 160 that is mounted on the head, a trunk portion 162 of the linear shape extending in a first direction perpendicular to the upper and and is perpendicular to the upper, at least extending in a second direction different from the first direction and a branch portion 161 of the linear two, the lower end of the probe mounting portion 161a is characterized by that is projecting, tapered from the lower surface of the branch portion 161 or the core 162.少なくとも2個のプローブ装着部161aを有し、プローブ装着部161aに先端から光を照射する送光プローブ12、又は、先端から光を受光する受光プローブ13が上方から挿入されて、被検者の頭部に装着されるホルダ160であって、上方と垂直となる第一方向に伸びた直線状の基幹部162と、上方と垂直となり、かつ、第一方向と異なる第二方向に伸びた少なくとも2本の直線状の枝部161とを備え、プローブ装着部161aの下端部は、基幹部162又は枝部161の下面から突出し、先細となっていることを特徴とする。
