An endoscope comprising: an insertion section which is insertable in a body cavity; a bend section which is disposed on a distal end side of the insertion section and is constituted by coupling a plurality of bend pieces; a coupling section provided on the proximal end side of the insertion section; a rotary body (35, 36) which is rotatably supported in the coupling section; a wire for a bend operation of the bend section, which has a distal end portion connected to the bend section, and a proximal end portion extending toward a proximal end side of the insertion section and wound around the rotary body, wherein the wire is moved by rotational movement of the rotary body so that the bend section is bent at an angle according to an amount of the rotational movement of the rotary body; driving force transmission means which is provided in the coupling section, includes a working shaft (37, 38, 39, 40) that is operable in a linear direction, and a rack-and-pinion mechanism which converts linear movement of the working shaft to rotational movement of the rotary body; a driving source unit which is detachably coupled to the coupling section and includes driving force generating means for generating a driving force for bending the bend section; and operation means which is provided in the driving source unit, includes a driving shaft (60, 61) that is operable in a linear direction by the driving force from the driving force generating means, and linearly moves the working shaft, when the driving source unit and the coupling section are coupled, in accordance with an operation of the driving shaft that operates in the linear direction by the driving force from the driving force generating means, wherein the rack-and-pinion mechanism includes a pinion gear (35a, 36a) provided on the rotary body, and a rack portion (37a, 38a) formed on the working shaft and meshed with the pinion gear, wherein the drive force transmission means convert the linear movement of the working shaft to the rotational movement of the rotary body via the pinion gear and the rack portion meshed with each other. an insertion section which is insertable in a body cavity; a bend section which is disposed on a distal end side of the insertion section and is constituted by coupling a plurality of bend pieces; a coupling section provided on the proximal end side of the insertion section; a rotary body (35, 36) which is rotatably supported in the coupling section; a wire for a bend operation of the bend section, which has a distal end portion connected to the bend section, and a proximal end portion extending toward a proximal end side of the insertion section and wound around the rotary body, wherein the wire is moved by rotational movement of the rotary body so that the bend section is bent at an angle according to an amount of the rotational movement of the rotary body; driving force transmission means which is provided in the coupling section, includes a working shaft (37, 38, 39, 40) that is operable in a linear direction, and a rack-and-pinion mechanism which converts linear movement of the working shaft to rotational movement of the rotary body; a driving source unit which is detachably coupled to the coupling section and includes driving force generating means for generating a driving force for bending the bend section; and operation means which is provided in the driving source unit, includes a driving shaft (60, 61) that is operable in a linear direction by the driving force from the driving force generating means, and linearly moves the working shaft, when the driving source unit and the coupling section are coupled, in accordance with an operation of the driving shaft that operates in the linear direction by the driving force from the driving force generating means,