The invention concerns a device for regulating the relative angular speed between a magnetic structure and a resonator magnetically coupled to each other and forming an oscillator which defines a magnetic escapement. The magnetic structure includes at least one annular magnetic path at least partially formed of a magnetic material and the resonator includes at least one element for magnetic coupling to the annular magnetic path, this coupling element being formed of a magnetic material having a physical parameter correlated to the magnetic potential energy of the oscillator. The radial dimension of the annular magnetic path is smaller than a corresponding dimension of the coupling element, and the magnetic material is arranged so that the physical parameter of said magnetic material gradually increases angularly or gradually decreases angularly in order to obtain an angularly extended magnetic potential energy area in each angular period of the annular magnetic path.