A steerable instrument for endoscopic and/or invasive type of applications, such as in surgery, which has an elongated tubular body having a proximal end part with a first actuation flexible zone having a first diameter and a distal end part having a first distal flexible zone having a second diameter that is different from the first diameter. A cylindrical diameter adaptation section is arranged to connect the proximal end part to the distal end part such that a flexion in a radial direction relative to a longitudinal center axis of the longitudinal tubular body of the first actuation flexible zone results in an amplified or attenuated flexion of the first distal flexible zone.
