Or light transmitting probe 12, and a probe mounting part 61a of the two, is irradiated with light from the tip to the probe mounting section 61a, a light receiving probe 13 for receiving the light from the tip is inserted, the head of the subject at least A holder 60 is mounted on, the branch portion 61 of the linear two, subject at least a core portion 62 of the linear extending in the first direction, extending in a second direction different from the first direction and characterized in that it sets the first specific point of the head, and a placement reference point 63a is disposed to coincide with the first specific point.少なくとも2個のプローブ装着部61aを有し、プローブ装着部61a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が挿入されて、被検者の頭部に装着されるホルダ60であって、第一方向に伸びた直線状の基幹部62と、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61と、被検者の頭部に第一特定点を設定し、第一特定点と一致するように配置される配置基準点63aとを備えることを特徴とする。
