An inserting section 2 has: an objective optical system 31 that is a side-viewing observation optical system； and an optical element 33 that is set further toward the inserting section base end side than the position of an observation window 21. The optical element 33 has: an output surface 33b that totally reflects a part of illuminating light, which has been outputted from a light source, and which has been traveling in the longitudinal direction of the inserting section 2； and a sloped surface 33d, which reflects another part of the illuminating light, re-reflects the part of the illuminating light reflected by the output surface 33b, and outputs the light from output positions, said illuminating light having been outputted from the light source, and having been travelling in the longitudinal direction of the inserting section 2. A reflecting position P2 of the part of the illuminating light reflected by the output surface 33b, said reflecting position P2 being on the sloped surface 33d, is set further toward the leading end side of the inserting section 2 than a reflecting position P1 of the illuminating light, said reflecting position P1 being on the output surface 33b.
