The guide mechanism is provided with: a guide portion with a first guide surface, the first guide surface becomes a non-concave and smooth tapered shape toward the insertion direction； a mounting portion for detachably attaching the guide portion to the examination mirror； installation The structure enables the guide part to be detachably mounted to the guide mechanism and is integrated with the mounting part； and a variable support device to relatively change the distance between the mounting part and the mounting structure.引導機構具備：引導部，具有第1引導面，前述第1引導面朝向插入方向成為無凹凸且平滑的漸縮形狀；安裝部，用以將引導部可卸除地安裝在診察鏡；裝設構造，使引導部對引導機構可卸除地裝設，且，與安裝部一體化；及可變支撐裝置，使安裝部與裝設構造的間隔相對地改變。
