An endoscope includes a flat surface which is provided at a distal end of an inserter to be inserted into a subject and is approximately perpendicular to an axial direction of the inserter, an observation window which has a light entrance surface located at a position higher than the flat surface, a fluid injection nozzle which is positioned on the flat surface and injects fluid toward the observation window, a first inclined plane which faces the fluid injection nozzle and inclines such that whose height gradually increases from the flat surface toward the observation window, and a back-flow prevention member which is provided so as to prevent the fluid having been injected from the fluid injection nozzle and passed though the light entrance surface of the observation window flows backwardly from the flat surface toward the light entrance surface of the observation window.
