An electronic lock device configured to be externally mounted on a building door is provided, and being configured to operate a lock by moving a lock bolt of an associated lock case between a retracted position and a protruded position. The device includes an electrical motor and a transmission for connecting said electrical motor to the associated lock case. The transmission includes a rotatable shaft configured to be connected to a lock follower of the lock case, and a rotatable member being drivingly connected to the electrical motor and being connected to an engagement member being allowed to pivot upon rotation of the rotatable member, such that the engagement member is engaging with the rotatable shaft when the electrical motor is driving the rotatable member.