A steerable instrument (10) for endoscopic and/or invasive type of applications, such as in surgery, which has an elongated tubular body (18) having a proximal end part (11) with a first actuation flexible zone (14, 15) having a first diameter and a distal end part (13) having a first distal flexible zone (16, 17) having a second diameter that is different from the first diameter. A cylindrical diameter adaptation section (164) is arranged to connect the proximal end part (11) to the distal end part (13) 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 (14, 15) results in an amplified or attenuated flexion of the first distal flexible zone (16, 17).
