An endoscope comprising: an insertion portion to be inserted into a body; a distal end portion body provided in a distal end of the insertion portion; a treatment tool leading-out port formed in the distal end portion body; a connecting pipe that is mounted on the distal end portion body, a distal end of which is communicated with the treatment tool leading-out port; a treatment tool inserting tube having flexibility that is arranged in the insertion portion, a distal end of which is connected to the connecting pipe; and a fixing sleeve that is fitted outward on a connecting portion between the connecting pipe and the treatment tool inserting tube for fixation of the connecting portion, wherein the fixing sleeve comprises: a cylindrical sleeve body having a distal end, a proximal end and a sleeve center axis; characterised in that the fixing sleeve further comprises: an arc-shaped portion that is connected to a proximal end side of the sleeve body, is formed in an arc shape along a cylindrical surface of the sleeve body and has a center angle smaller than 180°; and a projection portion that is formed along a peripheral direction of the sleeve center axis on an inner peripheral surface of the arc-shaped portion in a radial inside of the sleeve center axis. an insertion portion to be inserted into a body; a distal end portion body provided in a distal end of the insertion portion; a treatment tool leading-out port formed in the distal end portion body; a connecting pipe that is mounted on the distal end portion body, a distal end of which is communicated with the treatment tool leading-out port; a treatment tool inserting tube having flexibility that is arranged in the insertion portion, a distal end of which is connected to the connecting pipe; and a fixing sleeve that is fitted outward on a connecting portion between the connecting pipe and the treatment tool inserting tube for fixation of the connecting portion, wherein the fixing sleeve comprises: a cylindrical sleeve body having a distal end, a proximal end and a sleeve center axis; characterised in that the fixing sleeve further comprises: an arc-shaped portion that is connected to a proximal end side of the sleeve body, is formed in an arc shape along a cylindrical surface of the sleeve body and has a center angle smaller than 180°; and a projection portion that is formed along a peripheral direction of the sleeve center axis on an inner peripheral surface of the arc-shaped portion in a radial inside of the sleeve center axis. a cylindrical sleeve body having a distal end, a proximal end and a sleeve center axis; characterised in that the fixing sleeve further comprises: an arc-shaped portion that is connected to a proximal end side of the sleeve body, is formed in an arc shape along a cylindrical surface of the sleeve body and has a center angle smaller than 180°; and a projection portion that is formed along a peripheral direction of the sleeve center axis on an inner peripheral surface of the arc-shaped portion in a radial inside of the sleeve center axis. an arc-shaped portion that is connected to a proximal end side of the sleeve body, is formed in an arc shape along a cylindrical surface of the sleeve body and has a center angle smaller than 180°; and a projection portion that is formed along a peripheral direction of the sleeve center axis on an inner peripheral surface of the arc-shaped portion in a radial inside of the sleeve center axis.