The adjustment device for a portable element includes: a first and second pair of first and second wire-shaped elements; a first adjustment unit mounted mobile on the first pair of wire-shaped elements and configured to: define two deviation paths of the first pair of wire-shaped elements and to separate the first and second wire-shaped elements of the first pair by a first distance X1, and define a first mechanical coupling means with the second pair of wire-shaped elements; and a second adjustment unit mounted mobile on the second pair of wire-shaped elements and configured to: define two deviation paths of the second pair of wire-shaped elements and to separate the first and second wire-shaped elements of the second pair by a second distance X2, and define a first mechanical coupling means with the first pair of wire-shaped elements.