Access device provided with a folding door enabling secure communication between at least two zones of an enclosure

An access device enables controlled or secure communication between different areas of an enclosure, and in the example illustrated in the present application of an aircraft, while providing reduced size. The access device includes a folding door which, when in folded position, allows at least one of said openings to be closed and, when in deployed position, forms a security vestibule with at least one movable shutter allowing said opening created by the deployment of said folding door to be closed. By superimposing the main components of the security vestibule that said components allow to close, the device frees up the adjoining cabin space when the security vestibule is not in use.