The present invention relates to a movement for a timepiece comprising a power source (1, 22) mounted on a frame (24) and having a variable output torque as a function of its degree of winding. The power source is designed to maintain the oscillating movement of a mechanical oscillator (2, 3, 4) through a going train comprising a compensating device (5). The latter has an input connected kinematically to the power source, directly or via at least one wheel assembly, and an output connected kinematically to the mechanical oscillator, and is constructed so as to transmit a constant torque to the mechanical oscillator regardless of the degree of winding of the power source.; To this end, the compensating device comprises a cam (12, 84) whose periphery, which is of variable radius, extends approximately in a general plane, the variations of the radius of said cam being a function of the variations of the output torque of said power source, and said cam also having peripheral teeth. The compensating device further comprises an intermediate connecting mechanism (9, 10, 13, 83) so designed as to mesh with the teeth of said cam and provide a kinematic connection with little or no slip between said periphery of the cam and said going train.