The invention concerns a positioning device for a tube cleaning element rotatably driven by fluid passing through the tube. This is particularly useful for heat exchanger tubes. This device includes an open-frame support member (1) having one or more parts (8a, 8b) (preferably of generally cylindrical shape) for mounting on the outside on one end of said tube, and further includes a spindle (2) mounted for rotation with respect to said frame (1) along the axis of the end of said tube and adapted to be fastened to said rotatable element.