With an endoscope (1) including an inserted portion (2) that is inserted into the body of a patient, securing means (3) for securing the inserted portion (2) to tissue (A) inside the body, the securing means (3) being provided at least at a distal-end portion of the inserted portion (2), an observation optical system (4) that is provided at the inserted portion (2) and that acquires an image of the tissue (A), and observation-distance adjusting means (5) for adjusting the distance between the observation optical system (4) and a surface of the tissue(A), 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.
