A device for driving a flexible lance for cleaning a heat exchanger duct or the like, includes a frame in which a driving mechanism is arranged for moving this flexible lance in a driving direction in the direction of an outlet opening. The driving mechanism is provided with a clamp member which can be clamped on the flexible lance and which is movable in the frame towards and away from this outlet opening. The clamp member is mounted on an endless drive element. The active part of the endless drive runs parallel to the driving direction. The drive mechanism further comprises at least one non-driven counter roller arranged opposite said clamp member. The lance is clamped between the clamp member and the counter roller.