A film winding system of a camera, capable of automatically winding a film roll, comprising, an electric motor driven so as to winding the film roll, a film winding apparatus driven by the motor, a lock mechanism for locking the film winding apparatus, the lock mechanism comprising a film winding controller connected with the film winding apparatus and a lock lever engaging with the film winding controller so as to restrain an operation of the film winding apparatus, a releasing lever for cancelling an engagement of the lock lever to the film winding controller in advance before the film winding apparatus is actuated, and a loosing mechanism driven by the motor for reducing a degree of the engagement between the film winding controller and the lock lever in advance before the releasing lever swings in the cancellation direction of the engagement.The system operates as follows. Since the loosing mechanism is driven so as to reduce the degree of the engagement between the film winding controller and the lock lever in advance before the releasing lever swings in the cancellation direction of the engagement, the releasing lever cancels the engagement of the lock lever to the film winding controller with light dynamic force. Then, the film winding apparatus is actuated, and the film roll is wound.