An actuator device for a bicycle gearshift, comprising an actuation kinematic mechanism adapted to be deformed in order to move a derailleur of the gearshift; a driving member adapted to control the deformation of the aforementioned kinematic mechanism, the driving member comprising a motor and a threaded drive shaft put in rotation by the motor; a nut associated with the aforementioned kinematic mechanism and with the drive shaft. The actuator device comprises a snap mechanism that, in a first operative configuration, holds the nut in an engaged condition with the drive shaft such that the rotation of the drive shaft causes the deformation of the actuation kinematic mechanism and that, when the actuator device is subjected to a force greater than a predetermined threshold force, defines a release configuration in the nut, such that the rotation of the drive shaft does not cause the deformation of the actuation kinematic mechanism.