With an endoscope including a long, thin inserted portion that is inserted into the body of a patient, securing means for securing the inserted portion to tissue inside the body, the securing means being provided at least at a distal-end portion of the inserted portion, an observation optical system that is provided at the inserted portion and that acquires an image of the tissue, and observation-distance adjusting means for adjusting the distance between the observation optical system and a surface of the tissue, it is possible to attain a stable field of view without having to stop the pulsation or the like of the heart or other tissue.
