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 at least three mobile walls able to move, independently from one another, to form a closed cylinder, the walls thus being in a so-called security vestibule position, and to overlap at least in twos in order to close off access to one or more areas while concealing the security vestibule, the walls thus being in a so-called retracted position. By overlapping at the access level of said areas that the walls allow to close, the device frees up the adjoining cabin space.