This invention refers to an automatic locking device for shutters in fully open position, which comprises a support bracket provided with wall fixing means, with a tubular cursor that is inserted and slides outside the support bracket, being provided with a collapsible bascule element and a fixed counter-element on the back; it being provided that the point of the support bracket is shaped in such a way as to co-operate with the collapsible element to cause the automatic raising and stable stop in vertical position when the cursor slides backwards.