The invention relates to an adjusting device for adjusting two parts (2,3) with respect to one another that is used as a cam shaft adjuster. The objective of the invention is, with an easy and smooth operability, to ensure a self-locking and an at least extensive play-free, continuous adjustment of the two parts with a high degree of efficiency. To this end, the adjusting device comprises a first part (2) with webs (2.3, 22.3), which are interspaced in the peripheral direction and between which chambers (2.4) are formed, and includes a second part (3) with an internal gearing (3.2, 13.2), and a number of teeth (7, 27) that are arranged inside the chambers (2.4) while being interspaced in the peripheral direction. The adjusting device also includes an inner contact surface (7.4) for resting against an eccentric drive element (6), and includes an outer contact surface (7.5) for engaging inside the internal gearing (3.2, 13.2). When an input shaft (4) is rotated by the teeth (7, 27) located inside the chambers (2.4), rotational motions about rotation axes, which are parallel to a rotation axis (A) of the parts (2,3) can be executed.