Abstract: The invention relates to an extending, folding ladder comprising a single post (1) which is disposed in the symmetry plane thereof and which is formed by an assembly of segments (2) and adjacent segments (3) of the same length, each segment and the corresponding adjacent segment being articulated with one another at the midpoint thereof. In addition, the ends of consecutive segments are articulated with one another, such that the distances between two successive articulations are identical. The inventive ladder is deployed by manually extending the constituent parallelograms until the ladder is fully extended and said process is performed in reverse in order to retract the ladder for storage. The rungs (4) of the ladder are positioned at the midpoint articulation between two opposing segments or at each articulation between two successive segments on the front face of the ladder. The articulations between two successive segments on the rear face of the ladder are not equipped with rungs.