An endoscope includes a light source, an objective optical system, an optical system mover, a light amount detector, and a subject image generator. The light source emits illuminating light on a subject, and the reflected light of the illuminating light reflected on the subject, enters an objective optical system. The optical system mover moves the objective optical system in a direction of an optical axis of the objective optical system. The light amount detector detects the amount of the reflected light. The subject image generator generates image signals of the subject based on the reflected light. When an amount of the reflected light entering the objective optical system decreases, the optical system mover moves the objective optical system farther from the subject, and when an amount of the reflected light entering the objective optical system increases, the optical system mover moves the objective optical system closer to the subject, so that the objective optical system is focused on the subject.
