An endoscope apparatus includes: a light source that radiates a pulsed light beam onto an imaging subject; an imaging optical system; an image transmission optical system that transmits the image of the imaging subject; an optical sensor that has a light receiving surface on which a plurality of pixels are arrayed and that detects a light level of the image; and one or more processors, wherein the optical sensor obtains light levels by detecting, in a time division manner, a reflected light beam of the pulsed light beam at each of the pixels, and wherein the processors are configured to: calculate an observation distance to the imaging subject from the imaging optical system on a basis of the light levels.