In an endoscope, a flexible device of an elongated tube has a variable stiffness device. The variable stiffness device includes a movable control wire and a coil spring, to which compression force is applied to change stiffness. There occur changes in stiffness of the flexible device in plural radial directions of the coil spring at an equal point in an axial direction. The variable stiffness device is so constructed that a difference between maximum and minimum levels of stiffness of the variable stiffness device is set at most 0.2 time as much as stiffness of the flexible device with internal structures other than the variable stiffness device. Thus, unexpected grip feeling in manipulation of an operator at the time of advance can be removed in relation to undulating motion of the coil spring.