To provide an optical adapter for an endoscope which brightly and uniformly illuminates an object to be observed positioned on the side and also whose diameter is made small, and an endoscopic device using the same.

In the optical adapter for the endoscope 60 attached to/detached from a tip part 21 of the endoscope and having a side imaging optical system 71 and a side illumination optical system 81, the side illumination optical system 81 is equipped with a light guiding member for guiding a laser beam emitted from the tip part of the endoscope, and an illumination part 84 having a fluorescent member for stimulating light of prescribed wavelength with the laser beam guided by the light guiding member and emitting the light of prescribed wavelength to the object to be observed, and the side imaging optical system 71 is equipped with an incident part 72 making return light from the object to be observed incident, then the illumination parts 84 are arranged on both sides in the width direction of the incident part 72.