Collapsible straight ladder for lift shafts comprising - two side beams (1, 2) in the form of U-profile-limbs (1.1, 2.1) and - one-piece rungs which, with one of their ends are linked to the side beam (1, 2) in form of swivel joints, and with their other ends are pivotally linked to the side beams (1, 2) such, that the side beams (1, 2) are adjustable relative to each other in both directions wherein - the U-profile limbs (2.1) of the first side beams into which the one-piece rungs in the collapsed condition of the straight ladder, are retractable have a height which is adapted to the height of the rungs, whereas the U-profile limbs of the (1.1) of the second opposed side beams have a lower height than the U-profile limbs (2.1) of the first side beam characterized in that - the one-piece rungs are linked with both ends to the side beams(1.2) in form of swivel joints, that - the one-piece rungs have the forms of U-profiles, - the U-profile limbs (3.2; 3.3) of the one-piece rungs are linked with both ends to the side beam (1, 2) in the form of swivel joints - that the U-profile limbs (3.2; 3.3) of the one-piece rungs are inclined with the same angle relatively to the U-profile base (3.1) and - that the pivot points of the one-piece rungs at the side beams (1, 2), in the region of the front side of the rungs adjoining the U-profile limbs (3.2) have a smaller distance from the rung tread forming base (3.1) than the pivot points in the region of the rear rung side adjoining the U-profile limbs (3.3) and that - the U-profiles of the one-piece rungs adjoining the rung ends are provided with recesses (3.11; 3.12; 3.31; 3.32) which prevent a mutual interference of the rung ends in the collapsed, i.e. abutting position of the side beams (1, 2) and furthermore finger bruises. - two side beams (1, 2) in the form of U-profile-limbs (1.1, 2.1) and - one-piece rungs which, with one of their ends are linked to the side beam (1, 2) in form of swivel joints, and with their other ends are pivotally linked to the side beams (1, 2) such, that the side beams (1, 2) are adjustable relative to each other in both directions wherein - the U-profile limbs (2.1) of the first side beams into which the one-piece rungs in the collapsed condition of the straight ladder, are retractable have a height which is adapted to the height of the rungs, whereas the U-profile limbs of the (1.1) of the second opposed side beams have a lower height than the U-profile limbs (2.1) of the first side beam - the one-piece rungs are linked with both ends to the side beams(1.2) in form of swivel joints, that - the one-piece rungs have the forms of U-profiles, - the U-profile limbs (3.2; 3.3) of the one-piece rungs are linked with both ends to the side beam (1, 2) in the form of swivel joints - that the U-profile limbs (3.2; 3.3) of the one-piece rungs are inclined with the same angle relatively to the U-profile base (3.1) and - that the pivot points of the one-piece rungs at the side beams (1, 2), in the region of the front side of the rungs adjoining the U-profile limbs (3.2) have a smaller distance from the rung tread forming base (3.1) than the pivot points in the region of the rear rung side adjoining the U-profile limbs (3.3) and that - the U-profiles of the one-piece rungs adjoining the rung ends are provided with recesses (3.11; 3.12; 3.31; 3.32) which prevent a mutual interference of the rung ends in the collapsed, i.e. abutting position of the side beams (1, 2) and furthermore finger bruises.