Electronic device for driving a lock , comprising: - a support for connection with the cylinder of an existing lock having at least one through opening for accommodating a projecting portion of said cylinder , and fastening means to block the support with respect to said projecting portion; - a gear motor provided with an actuator and a transmission configured to rotate said cylinder and allow the opening or closing of the lock ; wherein the actuator is defined by an electric motor having an axis of rotation (B) parallel and offset with respect to a central axis (A) of said through opening so as to be parallel to the cylinder , and said transmission comprises at least a first and a second wheels rotatably connected to each other, wherein the first wheel is rigidly connected to the motor and the second wheel has a coupling portion with a shaft or tang of the cylinder ; said coupling portion being defined by a hole which can be coupled to said shaft or tang of the cylinder , and shaped with a non-circular cross-section complementarity shaped with respect to said shaft or tang of the cylinder , so as to allow its insertion into the hole preventing its relative rotation; - control board associated with said actuator , arranged to receive a driving signal from a user and configured to send to said actuator a signal representative of an opening or a closing of the lock in order to move the actuator; characterized in that it comprises a box body having at least a first plate and a second plate facing each other, defining an internal housing for said transmission and both provided with respective through holes substantially aligned with said coupling portion of the second wheel , wherein said actuator and said support are connected to said first plate , said transmission is located in said housing and said control board is connected to said second plate . - a support for connection with the cylinder of an existing lock having at least one through opening for accommodating a projecting portion of said cylinder , and fastening means to block the support with respect to said projecting portion; - a gear motor provided with an actuator and a transmission configured to rotate said cylinder and allow the opening or closing of the lock ; wherein the actuator is defined by an electric motor having an axis of rotation (B) parallel and offset with respect to a central axis (A) of said through opening so as to be parallel to the cylinder , and said transmission comprises at least a first and a second wheels rotatably connected to each other, wherein the first wheel is rigidly connected to the motor and the second wheel has a coupling portion with a shaft or tang of the cylinder ; said coupling portion being defined by a hole which can be coupled to said shaft or tang of the cylinder , and shaped with a non-circular cross-section complementarity shaped with respect to said shaft or tang of the cylinder , so as to allow its insertion into the hole preventing its relative rotation; - control board associated with said actuator , arranged to receive a driving signal from a user and configured to send to said actuator a signal representative of an opening or a closing of the lock in order to move the actuator; <EOS>