The maximum hardness Hmax 2 of the flexible tube portion 13 A of the endoscope 2 A is set such that the substantial maximum hardness Hmax 2 when the overtube 70 is attached is equal to or less than the maximum hardness Hmax 1 of the flexible tube portion 13 of the endoscope 2 As shown in FIG. That is, the maximum hardness Hmax 2 of the flexible tube portion 13 A of the endoscope 2 A is set so as to be approximately equal to the hardness obtained by subtracting the hardness of the overtube 70 itself from the maximum hardness Hmax 1 of the flexible tube portion 13 of the endoscope 2 And the maximum hardness of the endoscope 2 not fitted with the overtube 70 and the maximum hardness of the endoscope 2 A to which the overtube 70 is attached are set to be substantially equal to each other in the endoscope 2, 2 A having the hardness changing function .内視鏡2Aの可撓管部13Aの最大硬度Hmax2は、オーバーチューブ70を装着したときの実質的な最大硬度Hmax2が内視鏡2の可撓管部13の最大硬度Hmax1と同等以下となるように設定されている。すなわち、内視鏡2Aの可撓管部13Aの最大硬度Hmax2は、内視鏡2の可撓管部13の最大硬度Hmax1からオーバーチューブ70自体の硬度分を減算した硬度と略等しくなるように設定されており、硬度変更機能を備える内視鏡2,2Aにおいて、オーバーチューブ70を装着しない内視鏡2の最大硬度と、オーバーチューブ70を装着した内視鏡2Aの最大硬度とを略同等としている。
