An endoscope system comprising: a first endoscope including a soft section that has a small-diameter portion and a large-diameter portion, wherein the small-diameter portion is a distal portion and the large-diameter portion is formed proximally to the small-diameter portion and whose outer diameter is larger than the outer diameter of the small-diameter portion, the outer diameter of the larger diameter portion being substantially the same over the entire length thereof, the soft section being included in an insertion unit; a second endoscope which shares the same light source unit or video processor with the first endoscope and whose soft section has substantially the same outer diameter over the whole length thereof, the soft section being included in the insertion unit; and a third endoscope which shares the same light source unit or video processor with the first endoscope and the second endoscope and whose soft section has substantially the same outer diameter over the whole length thereof and has the outer diameter smaller than the outer diameter of the soft section of the second endoscope the soft section being provided in the insertion unit, wherein: the outer diameter of the large-diameter portion of the soft section of the first endoscope is substantially identical to or smaller than the outer diameter of the soft section of the second endoscope and is larger than the outer diameter of the soft section of the third endoscope, and the outer diameter of the small-diameter portion of the soft section of the first endoscope is substantially identical to the outer diameter of the soft section of the third endoscope. a first endoscope including a soft section that has a small-diameter portion and a large-diameter portion, wherein the small-diameter portion is a distal portion and the large-diameter portion is formed proximally to the small-diameter portion and whose outer diameter is larger than the outer diameter of the small-diameter portion, the outer diameter of the larger diameter portion being substantially the same over the entire length thereof, the soft section being included in an insertion unit; a second endoscope which shares the same light source unit or video processor with the first endoscope and whose soft section has substantially the same outer diameter over the whole length thereof, the soft section being included in the insertion unit; and a third endoscope which shares the same light source unit or video processor with the first endoscope and the second endoscope and whose soft section has substantially the same outer diameter over the whole length thereof and has the outer diameter smaller than the outer diameter of the soft section of the second endoscope the soft section being provided in the insertion unit, wherein: the outer diameter of the large-diameter portion of the soft section of the first endoscope is substantially identical to or smaller than the outer diameter of the soft section of the second endoscope and is larger than the outer diameter of the soft section of the third endoscope, and the outer diameter of the small-diameter portion of the soft section of the first endoscope is substantially identical to the outer diameter of the soft section of the third endoscope. the outer diameter of the large-diameter portion of the soft section of the first endoscope is substantially identical to or smaller than the outer diameter of the soft section of the second endoscope and is larger than the outer diameter of the soft section of the third endoscope, and the outer diameter of the small-diameter portion of the soft section of the first endoscope is substantially identical to the outer diameter of the soft section of the third endoscope.