Endoscopic optical adapter freely attachable to and detachable from endoscope

An endoscopic optical adapter freely attachable to and detachable from a endoscope, comprising:

• an adapter-side observational optical system facing an endoscope-side observational optical system provided with a solid-state image device placed in a tip constituent member of the endoscope;
• an adapter-side illuminational optical system facing endoscope-side illuminational optical system provided in the tip constituent member;
• a unit body in which the adapter-side observational optical system is fixedly placed;
• an adapter body on which a hole potion with the adapter-side illuminational optical system placed therein, a first concave portion with the unit body placed therein while being free to rotate, and a second concave portion with at least a part of the tip constituent member placed therein are formed;
• a positioning portion which is provided in each of the adapter body and the tip constituent member and which adjusts the positional relationship between the tip constituent member and the adapter body to be a predetermined positional relationship;
• and
• a cover member which is placed covering the unit body and the adapter body, which forms a space for placing the adapter-side illuminational optical system, and which is provided with a first optical member and a second optical member facing the adapter-side observational optical system and the adapter-side illuminational optical system.