The invention relates to an internal osteodistraction device, which includes two fixing points (7, 8) for attachment to a bone in such a way that the distance between the fixing points can be increased in a controlled manner, and a magnetostrictive element (1) which produces a reciprocating mechanical motion in a changing magnetic field. The magnetostrictive element is configured for taking up solely a compressive or tensile force, such that the magnetostrictive element pushes a unidirectional movement permitting element which allows for an increase in the distance between the fixing points, and as the magnetostrictive element is in the process of returning to its original length, a second unidirectional movement permitting element allows the magnetostrictive element to resume its original length without changing a distance between the fixing points of the distraction device.