A timepiece (2) includes an actuator, which applies braking pulses to the balance, which has an electromechanical device (6) and an electric control circuit (8). The device (6) includes a flexible member (16), formed by an elastic blade (20) and a mechanical element (22) defining a braking pad, and an electromagnetic system (10) formed by a coil carried by the flexible member and by a permanent magnet rigidly connected to a support (18) of the electromechanical device. When an electric pulse is provided to the coil, an electromagnetic force of repulsion is engendered between the coil and the permanent magnet so the mechanical element moves to a position of contact with the balance. To stabilise the rest position of the flexible member, a magnetic element (26) is rigidly connected to the coil to exert a magnetic return force complementary to the force of the elastic blade is provided.