To provide a device for moving a member stepwise in a tube that is capable of determining the moving position accurately.

Movement is evaluated by at least one position encoder 9, which sends information about the position of a member placed at one end of a tubular element mounted for translation on a support body 6 for supporting the device. The tubular element is in the shape of a member carrier worm 5 with longitudinal toothed racks 5A and 5B disposed peripherally. The worm 5 is translated in relation to the support body 6 that supports it when a first toothed belt 17A mounted on the support body 6 functions. The first toothed belt 17A is driven by a motor 8 fixed on the support body 6 and is engaged with one rack 5A. The other rack 5B is in engagement with a second toothed belt 17B for synchronously driving the position encoder 9 fixed on the support body 6.