An endoscope comprising: an insertion part which is inserted into a body cavity, the insertion part having: a distal end surface, the distal end surface including an observation window, an illumination window (52, 54), an outer peripheral edge, and a nozzle which jets a cleaning fluid toward the observation window; an outer circumferential surface centered along a longitudinal axis of the insertion part; and a chamfered surface disposed between the outer peripheral edge and the outer circumferential surface and being circumferentially round-chamfered, wherein a center of the distal end surface lies on the longitudinal axis of the insertion part, and a distance between the center of the distal end surface and the outer peripheral edge is assumed as r, wherein the observation window and the illumination window (52, 54) are located in a vicinity of the outer peripheral edge, in a vicinity of the observation window which is a region sandwiched by two tangents drawn from the center of the distal end surface to the observation window, the chamfered surface is round-chamfered in a manner that as a distance between a central axis of the observation window and a point of a plurality of points along the outer circumferential surface increases, a radius of round-chamfer of the chamfered surface increases, and in a vicinity of the illumination window (52, 54) which is a region sandwiched by two tangents drawn from the center of the distal end surface to the illumination window (52, 54), the chamfered surface is round-chamfered in a manner that as a distance between a central axis of the illumination window (52, 54) and a point of a plurality of points along the outer circumferential surface increases, a radius of round-chamfer of the chamfered surface increases, characterized in that: a central position of each of the observation window and the illumination window (52, 54) is located on an outer side of a distance position of 0.5 × r from the center of the distal end surface; and wherein the chamfered surface is round-chamfered in a manner that the radius of round-chamfer becomes the smallest at the point closest to the observation window. an insertion part which is inserted into a body cavity, the insertion part having: a distal end surface, the distal end surface including an observation window, an illumination window (52, 54), an outer peripheral edge, and a nozzle which jets a cleaning fluid toward the observation window; an outer circumferential surface centered along a longitudinal axis of the insertion part; and a chamfered surface disposed between the outer peripheral edge and the outer circumferential surface and being circumferentially round-chamfered, a distal end surface, the distal end surface including an observation window, an illumination window (52, 54), an outer peripheral edge, and a nozzle which jets a cleaning fluid toward the observation window; an outer circumferential surface centered along a longitudinal axis of the insertion part; and a chamfered surface disposed between the outer peripheral edge and the outer circumferential surface and being circumferentially round-chamfered, wherein a center of the distal end surface lies on the longitudinal axis of the insertion part, and a distance between the center of the distal end surface and the outer peripheral edge is assumed as r, wherein the observation window and the illumination window (52, 54) are located in a vicinity of the outer peripheral edge, in a vicinity of the observation window which is a region sandwiched by two tangents drawn from the center of the distal end surface to the observation window, the chamfered surface is round-chamfered in a manner that as a distance between a central axis of the observation window and a point of a plurality of points along the outer circumferential surface increases, a radius of round-chamfer of the chamfered surface increases, and in a vicinity of the illumination window (52, 54) which is a region sandwiched by two tangents drawn from the center of the distal end surface to the illumination window (52, 54), the chamfered surface is round-chamfered in a manner that as a distance between a central axis of the illumination window (52, 54) and a point of a plurality of points along the outer circumferential surface increases, a radius of round-chamfer of the chamfered surface increases, characterized in that: a central position of each of the observation window and the illumination window (52, 54) is located on an outer side of a distance position of 0.5 × r from the center of the distal end surface; and wherein the chamfered surface is round-chamfered in a manner that the radius of round-chamfer becomes the smallest at the point closest to the observation window.