The invention relates to a timepiece mechanism comprising an oscillator (1) with a flexible pivot, and a stop device (6) for stopping the oscillator (1), the oscillator (1) comprising: a base (20) for attaching the oscillator (1) to a stationary or mobile frame of a timepiece movement; an oscillating member (3, 21, 4) intended to oscillate in rotation about a virtual axis of rotation (A), the oscillating member (3, 21, 4) comprising a radial element (31, 21, 4) with respect to the virtual axis of rotation (A), the radial element (31, 21, 4) comprising at least one stop element (5a; 5a, 5b); and a flexible pivot (2a, 2b) for suspending the oscillating member (3, 21, 4) from the base (20) and defining the virtual axis of rotation (A); the stop device (6) comprising: a stop member (7) with at least one
abutment (71); the stop member (7) being configured to be movable between an active position in which the at least one
abutment (71) engages with the at least one stop element (5a; 5a, 5b) to lock the oscillating member (3, 21, 4) in a predetermined position in which the elastic return force of the flexible pivot (2a, 2b) is non-zero, and an inactive position in which the at least one
abutment (71) is spaced apart from the path travelled by the at least one stop element (5a; 5a, 5b) during the oscillation of the oscillating member (3, 21, 4), the stop member (7) being configured such that, during the movement of the stop member (7) in a first direction from the inactive position to the active position, the at least one abutment (71) follows a circular trajectory centred about an axis parallel to the virtual axis of rotation (A), the at least one abutment (71) and the at least one stop element (5a; 5a, 5b) being configured so that, when the at least one abutment (71) engages with the at least one stop element (5a; 5a, 5b) to lock the oscillating member (3, 21, 4), the force exerted by the at least one abutment (71) on the at least one stop element (5a; 5a, 5b) is essentially tangential with respect to the rotational movement performed by the at least one stop element (5a; 5a, 5b) during the oscillation of the oscillating member (3, 21, 4), the stop member (7) being further configured to be returned from the active position to the inactive position in a second direction opposite to the first direction. The invention also relates to a timepiece movement comprising such a timepiece mechanism, and to a timepiece comprising such a timepiece movement.