A cylindrical endoscope hood configured to be mounted on a tip end portion in a longitudinal axis direction of an endoscope, the endoscope including an optical system including at least an observation optical system and a treatment system, the endoscope hood having both ends open, a base end side opening and a tip end side opening and comprising: an endoscope mounting unit having the base end side opening which is configured to be mounted on the tip end portion of the endoscope; and a hood main body having the tip end side opening which has an outer diameter smaller than that of the base end side opening, the outer diameter of the tip end side opening being perpendicular to the longitudinal axis direction of the endoscope, wherein when the base end side opening is mounted on the tip end portion of the endoscope, the optical system and the treatment system are located on the inside of the tip end side opening when the tip end portion of the endoscope is viewed in the longitudinal axis direction of the endoscope, wherein a cross section in a longitudinal axis direction of the hood main body has ridge lines, at least one of the ridge lines including a tapered portion tapering off toward the tip end side opening, wherein the cross section in the longitudinal axis direction of the hood main body has a ridge line, the ridge line including a linear portion which is substantially parallel to a central axis of the endoscope, the linear portion being opposite to the tapered portion of the hood main body, wherein the tapered portion has an outer surface inclination angle that is a maximum value of an angle between an outer surface of the hood main body and the longitudinal axis direction of the hood main body, wherein the tapered portion has an inner surface inclination angle between an inner surface of the hood main body and the longitudinal axis direction of the hood main body that is smaller than the outer surface inclination angle, wherein the inner surface inclination angle of the tapered portion is equal to an inner surface inclination angle of the linear portion, wherein the tapered portion projects from the linear portion toward the tip end side in the longitudinal axis direction of the hood main body, and wherein the tip end side opening of the hood main body has at least one inclined portion at an angle with respect to a direction perpendicular to the longitudinal axis direction of the hood main body. an endoscope mounting unit having the base end side opening which is configured to be mounted on the tip end portion of the endoscope; and a hood main body having the tip end side opening which has an outer diameter smaller than that of the base end side opening, the outer diameter of the tip end side opening being perpendicular to the longitudinal axis direction of the endoscope, wherein when the base end side opening is mounted on the tip end portion of the endoscope, the optical system and the treatment system are located on the inside of the tip end side opening when the tip end portion of the endoscope is viewed in the longitudinal axis direction of the endoscope, wherein a cross section in a longitudinal axis direction of the hood main body has ridge lines, at least one of the ridge lines including a tapered portion tapering off toward the tip end side opening, wherein the cross section in the longitudinal axis direction of the hood main body has a ridge line, the ridge line including a linear portion which is substantially parallel to a central axis of the endoscope, the linear portion being opposite to the tapered portion of the hood main body, wherein the tapered portion has an outer surface inclination angle that is a maximum value of an angle between an outer surface of the hood main body and the longitudinal axis direction of the hood main body, wherein the tapered portion has an inner surface inclination angle between an inner surface of the hood main body and the longitudinal axis direction of the hood main body that is smaller than the outer surface inclination angle, wherein the inner surface inclination angle of the tapered portion is equal to an inner surface inclination angle of the linear portion, wherein the tapered portion projects from the linear portion toward the tip end side in the longitudinal axis direction of the hood main body, and wherein the tip end side opening of the hood main body has at least one inclined portion at an angle with respect to a direction perpendicular to the longitudinal axis direction of the hood main body.