Device (42; 84; 112; 152; 168; 172; 180; 190; 196; 210; 236; 260; 270; 280) for regulating the relative angular speed (ω) between a magnetic structure (44; 86; 114; 154; 198; 214; 240, 242) and a resonator (46; 116; 117; 119; 148; 158; 158A; 158B; 158C; 174; 182,184; 202; 238) which are magnetically coupled so as to define together an oscillator forming said regulating device, the magnetic structure including at least one annular magnetic path centred on an axis of rotation (51, 51A) of said magnetic structure or of the resonator, the magnetic structure and the resonator being arranged to undergo a rotation of one relative to the other about said axis of rotation when a drive torque is applied to the magnetic structure or to the resonator; the resonator including at least one element for magnetic coupling (50; 126,127; 149; 164,165; 177,178; 230,231) to said annular magnetic path; said annular magnetic path being at least partially formed of a first magnetic material at least one physical parameter of which is correlated to the magnetic potential energy of the oscillator but different therefrom, said first magnetic material being arranged along the annular magnetic path such that the magnetic potential energy of the oscillator varies angularly in a periodic manner along said annular magnetic path and thus defines an angular period (Pe) of said annular magnetic path; said magnetic coupling element having an active end portion, located on the side of said magnetic structure, which is magnetically coupled to said annular magnetic path so that an oscillation along a degree of freedom of a resonant mode of the resonator is maintained within a range of useful drive torque applied to the magnetic structure or to the resonator and so that a determined integer number of periods of said oscillation occurs during said relative rotation in each angular period of the annular magnetic path, the frequency of said oscillation thus determining said relative angular speed; said resonator being arranged relative to said magnetic structure such that said active end portion of said magnetic coupling element is at least mostly superposed, in orthogonal projection to a general geometric surface defined by said annular magnetic path, on said annular magnetic path during substantially a first vibration in each period of said oscillation, and such that the travel of the magnetic coupling element during said first vibration is substantially parallel to said general geometric surface, the annular magnetic surface having a dimension along said degree of freedom which is greater than the dimension of said active end portion of said magnetic coupling element along said degree of freedom; the regulating device being arranged such that, within said useful drive torque range, said annular magnetic path and said magnetic coupling element define, in each angular period, as a function of their relative position defined by their relative angular position and the position of the coupling element along its degree of freedom, an area of accumulation of magnetic potential energy (63, 65) in the oscillator; said annular magnetic path and said magnetic coupling element being arranged such that the magnetic coupling element receives, during said relative rotation, impulses along its degree of freedom about a rest position of said magnetic coupling element, said impulses defining, as a function of said relative position of the magnetic coupling element and of the annular magnetic path and for said range of useful drive torque delivered to the regulating device, impulse areas (68, 69), which are substantially located in a central impulse area adjacent to the areas of magnetic potential energy accumulation; the regulating device being characterized in that said first magnetic material is arranged in each angular period such that, at least in one area of said first magnetic material at least partially magnetically coupled to said active end portion for relative positions of the magnetic coupling element with respect to the annular magnetic path corresponding to at least one portion of the magnetic potential energy accumulation area in said angular period, said physical parameter gradually increases angularly or gradually decreases angularly, said annular magnetic path and said magnetic coupling element being arranged such that the mean angular gradient of said magnetic potential energy in said accumulation areas is less than the mean gradient of said magnetic potential energy in said impulse areas along said degree of freedom and in a same unit.