In an endoscope (12), a flexible device (22) of an elongated tube (10) has a variable stiffness device (35). The variable stiffness device (35) includes a movable control wire (31) and a coil spring (33), to which compression force is applied to change stiffness. There occur changes in stiffness of the flexible device (22) in plural radial directions (RD) of the coil spring (33) at an equal point in an axial direction (AD). The variable stiffness device (35) is so constructed that a difference between maximum and minimum levels of stiffness of the variable stiffness device (35) is set at most 0.2 time as much as stiffness of the flexible device (22) with internal structures other than the variable stiffness device (35). 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 (33).
