Step comprising: - a front plane comprising a pair of front uprights and at least one step connecting the front uprights, - a railing mounted on the front plane, this railing comprising a pair of side barriers (24, 25), each mounted in articulated fashion on a front upright between a deployed position in which each barrier (24, 25) extends essentially perpendicular to the front plane and a folded position in which each barrier (24, 25) extends essentially parallel to the front plane, - a rear plane mounted in articulated fashion on the front plane and comprising a pair of rear uprights and at least one bar connecting the rear uprights, the rear uprights ending in ends which, with ends of the front uprights, define a standing plane for the step in an unfolded position of the latter, in which the rear plane forms an angle with the front plane, - a pair of retractable rear wheels mounted so as to be able to move with respect to the rear plane between a retracted position in which the rear wheels extend above the standing plane and a deployed position in which the rear wheels project downwards beyond the standing plane, each rear wheel being urged towards its deployed position by a spring, - a front undercarriage equipped with at least one retractable front wheel, the front undercarriage being mounted so as to be able to move with respect to the front plane between a retracted position in which the front wheel extends above the standing plane and a deployed position in which the front wheel projects downwards beyond the standing plane, - a mechanism for activating the front undercarriage, this step being characterized in that the activating mechanism comprises at least one actuating lever mounted in articulated fashion on a front upright in line with a movable part of a barrier and a rod coupling the lever to the front undercarriage such that, in the folded position, the barrier places, via the lever, the front undercarriage in its deployed position. - a front plane comprising a pair of front uprights and at least one step connecting the front uprights, - a railing mounted on the front plane, this railing comprising a pair of side barriers (24, 25), each mounted in articulated fashion on a front upright between a deployed position in which each barrier (24, 25) extends essentially perpendicular to the front plane and a folded position in which each barrier (24, 25) extends essentially parallel to the front plane, - a rear plane mounted in articulated fashion on the front plane and comprising a pair of rear uprights and at least one bar connecting the rear uprights, the rear uprights ending in ends which, with ends of the front uprights, define a standing plane for the step in an unfolded position of the latter, in which the rear plane forms an angle with the front plane, - a pair of retractable rear wheels mounted so as to be able to move with respect to the rear plane between a retracted position in which the rear wheels extend above the standing plane and a deployed position in which the rear wheels project downwards beyond the standing plane, each rear wheel being urged towards its deployed position by a spring, - a front undercarriage equipped with at least one retractable front wheel, the front undercarriage being mounted so as to be able to move with respect to the front plane between a retracted position in which the front wheel extends above the standing plane and a deployed position in which the front wheel projects downwards beyond the standing plane, - a mechanism for activating the front undercarriage, this step being characterized in that the activating mechanism comprises at least one actuating lever mounted in articulated fashion on a front upright in line with a movable part of a barrier and a rod coupling the lever to the front undercarriage such that, in the folded position, the barrier places, via the lever, the front undercarriage in its deployed position.